Create common hooks structure shared between driver and cc1

This patch implements a target hooks structure for hooks shared
between the driver and the core compilers.  Such hooks go in
libcommon-target.a which is then linked into the relevant binaries.
ALWAYS_STRIP_DOTDOT is converted to a hook as the initial hook for the
new structure.

Bootstrapped with no regressions on x86_64-unknown-linux-gnu.  Also
tested building cc1 and xgcc for cross to hppa2.0w-hp-hpux11.23
(pa/som.h was the only header defining ALWAYS_STRIP_DOTDOT; note that
pa/t-pa previously was not used by any target, hence the complete
replacement of its contents).  OK to commit?

The general structure for these hooks is as described in
<http://gcc.gnu.org/ml/gcc-patches/2011-04/msg00434.html>, the
description of the patch that separated the C-family hooks structure
more cleanly from the main hooks.  In particular, the common/ and
common/config/ directories are used as described there.  I don't plan
to work on moving "common" files to the common/ directory but would
certainly encourage people to do so (and likewise to set up the
driver/ directory); files that should move include the sources of
libcommon.a and libcommon-target.a, and opts.c and params.c (which
will end up being used in libcommon-target.a), and *most* of the
headers used by those files.

(flags.h is a mess and should not I think be considered common; some
declarations should perhaps move to opts.h or tree.h.  The
SWITCHABLE_TARGET bits of flags.h, in particular, represent a hidden
dependency on tm.h (if tm.h isn't included first, flags.h will quietly
produce the wrong declarations), and a reason the header should not be
included in common or driver code; while cc1-only code generally uses
flags.h instead of options.h, maybe options.h should actually be more
widely used instead and flags.h should #error if used without tm.h.
coretypes.h isn't strictly common - many types defined there should
properly only be visible in the core compilers - but I think can
reasonably be treated as common initially.)

I *do* plan to move all the target hooks used in opts.c to the new
structure.

The following target macros used in both the driver (including cc1)
and the core compilers should I think end up in the new structure
(some are currently used in code built for the target so would need
extra work arranging for the compiler to predefine macros based on
them if -fbuilding-libgcc): NAME__MAIN NEXT_OBJC_RUNTIME
NO_DOLLAR_IN_LABEL NO_DOT_IN_LABEL STANDARD_EXEC_PREFIX
TARGET_EXECUTABLE_SUFFIX TARGET_OBJECT_SUFFIX USER_LABEL_PREFIX.  The
same applies to the following macros used in opts.c:
DEFAULT_GDB_EXTENSIONS DEFAULT_SIGNED_CHAR STACK_CHECK_BUILTIN
STACK_CHECK_STATIC_BUILTIN.  TARGET_64BIT is a special case that is
wrongly used in target-independent code but should be private to
particular ports.

The following target macros are used in both the driver and the core
compilers, but probably can't become hooks because of the ways they
are used: DBX_DEBUGGING_INFO DWARF2_DEBUGGING_INFO
PREFERRED_DEBUGGING_TYPE XCOFF_DEBUGGING_INFO.  Making them into
configure-defined macros (with different names for the sake of
poisoning) is probably appropriate; they are set by logic based on
combinations of target cases in config.gcc, configure options to
select particular formats that contribute entries to tm_file, and
toplevel configure.ac code(!)  that defaults --with-stabs on for
certain targets, and much simpler logic is probably appropriate in
practice (i.e. first follow configure options, failing that default to
DWARF2 except for a list of targets deliberately choosing other
formats, and similarly control what set of formats have support built
in).

2011-05-24  Joseph Myers  <joseph@codesourcery.com>

	* common/common-target-def.h, common/common-target.def,
	common/common-target.h, common/config/default-common.c,
	common/config/pa/pa-common.c: New files.
	* Makefile.in (EXTRA_COMMON_OBJS, COMMON_TARGET_DEF,
	COMMON_TARGET_H, COMMON_TARGET_DEF_H): New.
	(OBJS-libcommon-target): Include $(EXTRA_COMMON_OBJS).
	(prefix.o): Update dependencies.
	(default-common.o, common/common-target-hooks-def.h,
	s-common-target-hooks-def-h): New.
	(s-tm-texi): Also check timestamp on common-target.def.
	(build/genhooks.o): Update dependencies.
	* config.gcc (extra_common_objs, target_has_targetm_common):
	Define.
	(hppa*-*-*): Add pa/t-pa to tmake_file.
	* config/pa/som.h (ALWAYS_STRIP_DOTDOT): Replace with
	TARGET_ALWAYS_STRIP_DOTDOT.
	* config/pa/t-pa: Remove previous contents.
	(pa-common.o): New.
	* configure.ac (extra_common_objs): Substitute.
	(common): Create directory.
	* configure: Regenerate.
	* doc/tm.texi.in (targetm_common): Document.
	(TARGET_ALWAYS_STRIP_DOTDOT): Add @hook entry.
	* doc/tm.texi: Regenerate.
	* genhooks.c (hook_array): Also include common/common-target.def.
	* prefix.c (tm.h): Don't include.
	(common/common-target.h): Include.
	(ALWAYS_STRIP_DOTDOT): Don't define.
	(update_path): Use targetm_common.always_strip_dotdot instead of
	ALWAYS_STRIP_DOTDOT.
	* system.h (ALWAYS_STRIP_DOTDOT): Poison.

Create common hooks structure shared between driver and cc1

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Patch