replace LIBGCC2_WORDS_BIG_ENDIAN with __BYTE_ORDER__

diff --git a/gcc/config/arc/arc.h b/gcc/config/arc/arc.h
index f2d273d..bb47224 100644
--- a/gcc/config/arc/arc.h
+++ b/gcc/config/arc/arc.h
@@ -99,14 +99,6 @@  extern int arc_cpu_type;
    numbered.  */
 #define WORDS_BIG_ENDIAN (TARGET_BIG_ENDIAN)
 
-/* Define this to set the endianness to use in libgcc2.c, which can
-   not depend on target_flags.  */
-#ifdef __big_endian__
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#endif
-
 /* Width of a word, in units (bytes).  */
 #define UNITS_PER_WORD 4
 
diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index c8cbfa2..0764285 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -560,14 +560,6 @@  extern int arm_arch_hwdiv;
    This is always false, even when in big-endian mode.  */
 #define WORDS_BIG_ENDIAN  (BYTES_BIG_ENDIAN && ! TARGET_LITTLE_WORDS)
 
-/* LIBGCC2_WORDS_BIG_ENDIAN has to be a constant, so we define this based
-   on processor pre-defineds when compiling libgcc2.c.  */
-#if defined(__ARMEB__) && !defined(__ARMWEL__)
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#endif
-
 /* Define this if most significant word of doubles is the lowest numbered.
    The rules are different based on whether or not we use FPA-format,
    VFP-format or some other floating point co-processor's format doubles.  */
diff --git a/gcc/config/dfp-bit.h b/gcc/config/dfp-bit.h
index f093785..142c56b 100644
--- a/gcc/config/dfp-bit.h
+++ b/gcc/config/dfp-bit.h
@@ -33,12 +33,8 @@  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #include "coretypes.h"
 #include "tm.h"
 
-#ifndef LIBGCC2_WORDS_BIG_ENDIAN
-#define LIBGCC2_WORDS_BIG_ENDIAN WORDS_BIG_ENDIAN
-#endif
-
 #ifndef LIBGCC2_FLOAT_WORDS_BIG_ENDIAN
-#define LIBGCC2_FLOAT_WORDS_BIG_ENDIAN LIBGCC2_WORDS_BIG_ENDIAN
+#define LIBGCC2_FLOAT_WORDS_BIG_ENDIAN (__BYTE_ORDER__ != __LITTLE_ENDIAN__)
 #endif
 
 #ifndef LIBGCC2_LONG_DOUBLE_TYPE_SIZE
diff --git a/gcc/config/fixed-bit.h b/gcc/config/fixed-bit.h
index ce5b96e..b75da67 100644
--- a/gcc/config/fixed-bit.h
+++ b/gcc/config/fixed-bit.h
@@ -41,14 +41,6 @@  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    Ex: If we define FROM_QQ and TO_SI, the conversion from QQ to SI is
    generated.  */
 
-/* Permit the tm.h file to select the endianness to use just for this
-   file.  This is used when the endianness is determined when the
-   compiler is run.  */
-
-#ifndef LIBGCC2_WORDS_BIG_ENDIAN
-#define LIBGCC2_WORDS_BIG_ENDIAN WORDS_BIG_ENDIAN
-#endif
-
 #ifndef LIBGCC2_LONG_DOUBLE_TYPE_SIZE
 #define LIBGCC2_LONG_DOUBLE_TYPE_SIZE LONG_DOUBLE_TYPE_SIZE
 #endif
@@ -428,7 +420,7 @@  typedef int word_type __attribute__ ((mode (__word__)));
 /* The following defines are based on the previous defines.  */
 
 #if defined (HINT_C_TYPE)
-#if LIBGCC2_WORDS_BIG_ENDIAN
+#if __BYTE_ORDER__ != __LITTLE_ENDIAN__
   struct INTstruct {HINT_C_TYPE high, low;};
 #else
   struct INTstruct {HINT_C_TYPE low, high;};
diff --git a/gcc/config/ia64/ia64.h b/gcc/config/ia64/ia64.h
index 98e9b64..8605592 100644
--- a/gcc/config/ia64/ia64.h
+++ b/gcc/config/ia64/ia64.h
@@ -148,12 +148,6 @@  extern enum processor_type ia64_tune;
 
 #define WORDS_BIG_ENDIAN (TARGET_BIG_ENDIAN != 0)
 
-#if defined(__BIG_ENDIAN__)
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#endif
-
 #define UNITS_PER_WORD 8
 
 #define POINTER_SIZE (TARGET_ILP32 ? 32 : 64)
diff --git a/gcc/config/iq2000/iq2000.h b/gcc/config/iq2000/iq2000.h
index 6e670ba..05b02f7 100644
--- a/gcc/config/iq2000/iq2000.h
+++ b/gcc/config/iq2000/iq2000.h
@@ -76,7 +76,6 @@ 
 #define BITS_BIG_ENDIAN 		0
 #define BYTES_BIG_ENDIAN 		1 
 #define WORDS_BIG_ENDIAN 		1
-#define LIBGCC2_WORDS_BIG_ENDIAN	1
 #define BITS_PER_WORD 			32
 #define MAX_BITS_PER_WORD 		64
 #define UNITS_PER_WORD 			4
diff --git a/gcc/config/lm32/lm32.h b/gcc/config/lm32/lm32.h
index b0c2d59..afe9a6b 100644
--- a/gcc/config/lm32/lm32.h
+++ b/gcc/config/lm32/lm32.h
@@ -84,7 +84,6 @@ 
 #define BITS_BIG_ENDIAN 0
 #define BYTES_BIG_ENDIAN 1
 #define WORDS_BIG_ENDIAN 1
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
 
 #define BITS_PER_UNIT 8
 #define BITS_PER_WORD 32
diff --git a/gcc/config/m32r/m32r.h b/gcc/config/m32r/m32r.h
index d767cb9..7bfc975 100644
--- a/gcc/config/m32r/m32r.h
+++ b/gcc/config/m32r/m32r.h
@@ -328,12 +328,6 @@  extern enum m32r_sdata m32r_sdata;
    numbered.  */
 #define WORDS_BIG_ENDIAN (TARGET_LITTLE_ENDIAN == 0)
 
-/* Define this macro if WORDS_BIG_ENDIAN is not constant.  This must
-   be a constant value with the same meaning as WORDS_BIG_ENDIAN,
-   which will be used only when compiling libgcc2.c.  Typically the
-   value will be set based on preprocessor defines.  */
-/*#define LIBGCC2_WORDS_BIG_ENDIAN 1*/
-
 /* Width of a word, in units (bytes).  */
 #define UNITS_PER_WORD 4
 
diff --git a/gcc/config/mcore/mcore.h b/gcc/config/mcore/mcore.h
index a149eb1..8efe64f 100644
--- a/gcc/config/mcore/mcore.h
+++ b/gcc/config/mcore/mcore.h
@@ -106,12 +106,6 @@  extern char * mcore_current_function_name;
    numbered.  */
 #define WORDS_BIG_ENDIAN (! TARGET_LITTLE_END)
 
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#ifdef __MCORELE__
-#undef  LIBGCC2_WORDS_BIG_ENDIAN
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#endif
-
 #define MAX_BITS_PER_WORD 32
 
 /* Width of a word, in units (bytes).  */
diff --git a/gcc/config/mep/mep.h b/gcc/config/mep/mep.h
index 07f0c85..1f51aa9 100644
--- a/gcc/config/mep/mep.h
+++ b/gcc/config/mep/mep.h
@@ -167,12 +167,6 @@  crtbegin.o%s"
 #define BYTES_BIG_ENDIAN (TARGET_LITTLE_ENDIAN ? 0 : 1)
 #define WORDS_BIG_ENDIAN (TARGET_LITTLE_ENDIAN ? 0 : 1)
 
-#ifdef __LITTLE_ENDIAN__
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#endif
-
 #define UNITS_PER_WORD 4
 
 #define PROMOTE_MODE(MODE, UNSIGNEDP, TYPE)	\
diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h
index 23dba7c..449c893 100644
--- a/gcc/config/mips/mips.h
+++ b/gcc/config/mips/mips.h
@@ -1290,14 +1290,6 @@  enum mips_code_readable_setting {
 #define BYTES_BIG_ENDIAN (TARGET_BIG_ENDIAN != 0)
 #define WORDS_BIG_ENDIAN (TARGET_BIG_ENDIAN != 0)
 
-/* Define this to set the endianness to use in libgcc2.c, which can
-   not depend on target_flags.  */
-#if !defined(MIPSEL) && !defined(__MIPSEL__)
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#endif
-
 #define MAX_BITS_PER_WORD 64
 
 /* Width of a word, in units (bytes).  */
diff --git a/gcc/config/rs6000/sysv4.h b/gcc/config/rs6000/sysv4.h
index 25584b2..6d88e32 100644
--- a/gcc/config/rs6000/sysv4.h
+++ b/gcc/config/rs6000/sysv4.h
@@ -258,14 +258,6 @@  do {									\
 #define	BYTES_BIG_ENDIAN (TARGET_BIG_ENDIAN)
 #define	WORDS_BIG_ENDIAN (TARGET_BIG_ENDIAN)
 
-/* Define this to set the endianness to use in libgcc2.c, which can
-   not depend on target_flags.  */
-#if !defined(__LITTLE_ENDIAN__) && !defined(__sun__)
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#endif
-
 /* Define cutoff for using external functions to save floating point.
    When optimizing for size, use external functions when profitable.  */
 #define FP_SAVE_INLINE(FIRST_REG) (optimize_size			\
diff --git a/gcc/config/rx/rx.h b/gcc/config/rx/rx.h
index 7da4de1..534da5f 100644
--- a/gcc/config/rx/rx.h
+++ b/gcc/config/rx/rx.h
@@ -96,12 +96,6 @@  extern enum rx_cpu_types  rx_cpu_type;
 #define BYTES_BIG_ENDIAN 		TARGET_BIG_ENDIAN_DATA
 #define WORDS_BIG_ENDIAN 		TARGET_BIG_ENDIAN_DATA
 
-#ifdef __RX_BIG_ENDIAN__
-#define LIBGCC2_WORDS_BIG_ENDIAN	1
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN	0
-#endif
-
 #define UNITS_PER_WORD 			4
 
 #define INT_TYPE_SIZE			32
diff --git a/gcc/config/score/score.h b/gcc/config/score/score.h
index 621f56e..a01ffed 100644
--- a/gcc/config/score/score.h
+++ b/gcc/config/score/score.h
@@ -106,14 +106,6 @@ 
 #define BYTES_BIG_ENDIAN       (TARGET_LITTLE_ENDIAN == 0)
 #define WORDS_BIG_ENDIAN       (TARGET_LITTLE_ENDIAN == 0)
 
-/* Define this to set the endianness to use in libgcc2.c, which can
-   not depend on target_flags.  */
-#if defined(__scorele__)
-#define LIBGCC2_WORDS_BIG_ENDIAN       0
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN       1
-#endif
-
 /* Width of a word, in units (bytes).  */
 #define UNITS_PER_WORD                 4
 
diff --git a/gcc/config/sh/sh.h b/gcc/config/sh/sh.h
index 8f149dc..145f496 100644
--- a/gcc/config/sh/sh.h
+++ b/gcc/config/sh/sh.h
@@ -518,14 +518,6 @@  extern enum sh_divide_strategy_e sh_div_strategy;
    numbered.  */
 #define WORDS_BIG_ENDIAN (TARGET_LITTLE_ENDIAN == 0)
 
-/* Define this to set the endianness to use in libgcc2.c, which can
-   not depend on target_flags.  */
-#if defined(__LITTLE_ENDIAN__)
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#endif
-
 #define MAX_BITS_PER_WORD 64
 
 /* Width in bits of an `int'.  We want just 32-bits, even if words are
diff --git a/gcc/config/sparc/sparc.h b/gcc/config/sparc/sparc.h
index ccb7dca..1955e99 100644
--- a/gcc/config/sparc/sparc.h
+++ b/gcc/config/sparc/sparc.h
@@ -585,14 +585,6 @@  extern struct sparc_cpu_select sparc_select[];
    numbered.  */
 #define WORDS_BIG_ENDIAN 1
 
-/* Define this to set the endianness to use in libgcc2.c, which can
-   not depend on target_flags.  */
-#if defined (__LITTLE_ENDIAN__) || defined(__LITTLE_ENDIAN_DATA__)
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#endif
-
 #define MAX_BITS_PER_WORD	64
 
 /* Width of a word, in units (bytes).  */
diff --git a/gcc/config/xtensa/xtensa.h b/gcc/config/xtensa/xtensa.h
index 7dc22a2..435c21a 100644
--- a/gcc/config/xtensa/xtensa.h
+++ b/gcc/config/xtensa/xtensa.h
@@ -94,12 +94,6 @@  extern unsigned xtensa_current_frame_size;
 #define EXTRA_SPECS							\
   { "subtarget_cpp_spec", SUBTARGET_CPP_SPEC },
 
-#ifdef __XTENSA_EB__
-#define LIBGCC2_WORDS_BIG_ENDIAN 1
-#else
-#define LIBGCC2_WORDS_BIG_ENDIAN 0
-#endif
-
 /* Show we can debug even without a frame pointer.  */
 #define CAN_DEBUG_WITHOUT_FP
 
diff --git a/gcc/cppbuiltin.c b/gcc/cppbuiltin.c
index 89b0f41..28634a5 100644
--- a/gcc/cppbuiltin.c
+++ b/gcc/cppbuiltin.c
@@ -138,6 +138,24 @@  define_builtin_macros_for_type_sizes (cpp_reader *pfile)
   cpp_define_formatted (pfile, "__BIGGEST_ALIGNMENT__=%d",
 			BIGGEST_ALIGNMENT / BITS_PER_UNIT);
 
+  /* Define constants useful for implementing endian.h.  */
+  cpp_define (pfile, "__LITTLE_ENDIAN__=1234");
+  cpp_define (pfile, "__BIG_ENDIAN__=4321");
+  cpp_define (pfile, "__PDP_ENDIAN__=3412");
+
+  if (WORDS_BIG_ENDIAN == BYTES_BIG_ENDIAN)
+    cpp_define_formatted (pfile, "__BYTE_ORDER__=%s",
+			  (WORDS_BIG_ENDIAN
+			   ? "__BIG_ENDIAN__"
+			   : "__LITTLE_ENDIAN__"));
+  else
+    {
+      /* Assert that we're only dealing with the PDP11 case.  */
+      gcc_assert (!BYTES_BIG_ENDIAN && WORDS_BIG_ENDIAN);
+
+      cpp_define (pfile, "__BYTE_ORDER__=__PDP_ENDIAN__");
+    }
+
   /* ptr_type_node can't be used here since ptr_mode is only set when
      toplev calls backend_init which is not done with -E switch.  */
   cpp_define_formatted (pfile, "__SIZEOF_POINTER__=%d",
diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi
index 7276b61..d14fa54 100644
--- a/gcc/doc/cpp.texi
+++ b/gcc/doc/cpp.texi
@@ -2265,6 +2265,29 @@  Defined to the number of bytes of the C standard data types: @code{int},
 @code{double}, @code{long double}, @code{size_t}, @code{wchar_t}, @code{wint_t}
 and @code{ptrdiff_t}.
 
+@item __BYTE_ORDER__
+@itemx __LITTLE_ENDIAN__
+@itemx __BIG_ENDIAN__
+@itemx __PDP_ENDIAN__
+@code{__BYTE_ORDER__} is defined to one of the values
+@code{__LITTLE_ENDIAN__}, @code{__BIG_ENDIAN__}, or
+@code{__PDP_ENDIAN__} to reflect the layout of multi-byte and
+multi-word quantities in memory.  If @code{__BYTE_ORDER__} is equal to
+@code{__LITTLE_ENDIAN__} or @code{__BIG_ENDIAN__}, then multi-byte and
+multi-word quantities are laid out identically: the byte (word) at the
+lowest address is the least significant or most significant byte
+(word) of the quantity, respectively.  If @code{__BYTE_ORDER__} is
+equal to @code{__PDP_ENDIAN__}, then bytes in 16-bit words are laid
+out in a little-endian fashion, whereas the 16-bit subwords of a
+32-bit quantity are laid out in big-endian fashion.
+
+You should use these macros for testing like this:
+
+@smallexample
+/* @r{Test for a little-endian machine} */
+#if __BYTE_ORDER__ == __LITTLE_ENDIAN__
+@end smallexample
+
 @item __DEPRECATED
 This macro is defined, with value 1, when compiling a C++ source file
 with warnings about deprecated constructs enabled.  These warnings are
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index a268617..ab4e893 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -938,13 +938,6 @@  order of words in memory is the same as the order in registers.  This
 macro need not be a constant.
 @end defmac
 
-@defmac LIBGCC2_WORDS_BIG_ENDIAN
-Define this macro if @code{WORDS_BIG_ENDIAN} is not constant.  This must be a
-constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be
-used only when compiling @file{libgcc2.c}.  Typically the value will be set
-based on preprocessor defines.
-@end defmac
-
 @defmac FLOAT_WORDS_BIG_ENDIAN
 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
 @code{TFmode} floating point numbers are stored in memory with the word
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 74cf927..23fa032 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -936,13 +936,6 @@  order of words in memory is the same as the order in registers.  This
 macro need not be a constant.
 @end defmac
 
-@defmac LIBGCC2_WORDS_BIG_ENDIAN
-Define this macro if @code{WORDS_BIG_ENDIAN} is not constant.  This must be a
-constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be
-used only when compiling @file{libgcc2.c}.  Typically the value will be set
-based on preprocessor defines.
-@end defmac
-
 @defmac FLOAT_WORDS_BIG_ENDIAN
 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
 @code{TFmode} floating point numbers are stored in memory with the word
diff --git a/gcc/libgcc2.h b/gcc/libgcc2.h
index d2d86ef..c95e263 100644
--- a/gcc/libgcc2.h
+++ b/gcc/libgcc2.h
@@ -35,14 +35,6 @@  extern void __clear_cache (char *, char *);
 extern void __eprintf (const char *, const char *, unsigned int, const char *)
   __attribute__ ((__noreturn__));
 
-/* Permit the tm.h file to select the endianness to use just for this
-   file.  This is used when the endianness is determined when the
-   compiler is run.  */
-
-#ifndef LIBGCC2_WORDS_BIG_ENDIAN
-#define LIBGCC2_WORDS_BIG_ENDIAN WORDS_BIG_ENDIAN
-#endif
-
 #ifndef LIBGCC2_LONG_DOUBLE_TYPE_SIZE
 #define LIBGCC2_LONG_DOUBLE_TYPE_SIZE LONG_DOUBLE_TYPE_SIZE
 #endif
@@ -407,9 +399,9 @@  extern TCtype __multc3 (TFtype, TFtype, TFtype, TFtype);
 #define int bogus_type
 
 /* DWstructs are pairs of Wtype values in the order determined by
-   LIBGCC2_WORDS_BIG_ENDIAN.  */
+   __BYTE_ORDER__.  */
 
-#if LIBGCC2_WORDS_BIG_ENDIAN
+#if __BYTE_ORDER__ != __LITTLE_ENDIAN__
   struct DWstruct {Wtype high, low;};
 #else
   struct DWstruct {Wtype low, high;};
diff --git a/gcc/system.h b/gcc/system.h
index 5131fed..ec0c796 100644
--- a/gcc/system.h
+++ b/gcc/system.h
@@ -785,7 +785,7 @@  extern void fancy_abort (const char *, int, const char *) ATTRIBUTE_NORETURN;
 	LANG_HOOKS_MISSING_ARGUMENT LANG_HOOKS_HASH_TYPES
 
 /* Hooks into libgcc2.  */
- #pragma GCC poison LIBGCC2_DOUBLE_TYPE_SIZE
+ #pragma GCC poison LIBGCC2_DOUBLE_TYPE_SIZE LIBGCC2_WORDS_BIG_ENDIAN
 
 /* Miscellaneous macros that are no longer used.  */
  #pragma GCC poison USE_MAPPED_LOCATION
diff --git a/libdecnumber/dconfig.h b/libdecnumber/dconfig.h
index 91aa334..f432377 100644
--- a/libdecnumber/dconfig.h
+++ b/libdecnumber/dconfig.h
@@ -28,12 +28,8 @@  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #include "coretypes.h"
 #include "tm.h"
 
-#ifndef LIBGCC2_WORDS_BIG_ENDIAN
-#define LIBGCC2_WORDS_BIG_ENDIAN WORDS_BIG_ENDIAN
-#endif
-
 #ifndef LIBGCC2_FLOAT_WORDS_BIG_ENDIAN
-#define LIBGCC2_FLOAT_WORDS_BIG_ENDIAN LIBGCC2_WORDS_BIG_ENDIAN
+#define LIBGCC2_FLOAT_WORDS_BIG_ENDIAN (__BYTE_ORDER__ != __LITTLE_ENDIAN__)
 #endif
 
 #if LIBGCC2_FLOAT_WORDS_BIG_ENDIAN
diff --git a/libgcc/config/libbid/bid_gcc_intrinsics.h b/libgcc/config/libbid/bid_gcc_intrinsics.h
index f5bd8d0..5c5dbba 100644
--- a/libgcc/config/libbid/bid_gcc_intrinsics.h
+++ b/libgcc/config/libbid/bid_gcc_intrinsics.h
@@ -30,12 +30,8 @@  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #include "coretypes.h"
 #include "tm.h"
 
-#ifndef LIBGCC2_WORDS_BIG_ENDIAN
-#define LIBGCC2_WORDS_BIG_ENDIAN WORDS_BIG_ENDIAN
-#endif
-
 #ifndef LIBGCC2_FLOAT_WORDS_BIG_ENDIAN
-#define LIBGCC2_FLOAT_WORDS_BIG_ENDIAN LIBGCC2_WORDS_BIG_ENDIAN
+#define LIBGCC2_FLOAT_WORDS_BIG_ENDIAN (__BYTE_ORDER__ != __LITTLE_ENDIAN__)
 #endif
 
 #ifndef LIBGCC2_LONG_DOUBLE_TYPE_SIZE