[libfortran] PR 47571 Fix bootstrap failure on alpha*-dec-osf*

diff --git a/libgfortran/acinclude.m4 b/libgfortran/acinclude.m4
index acd1d4d..92e0271 100644
--- a/libgfortran/acinclude.m4
+++ b/libgfortran/acinclude.m4
@@ -110,7 +110,7 @@  void foo (void);
 	      [Define to 1 if the target supports #pragma weak])
   fi
   case "$host" in
-    *-*-darwin* | *-*-hpux* | *-*-cygwin* | *-*-mingw* )
+    *-*-darwin* | *-*-hpux* | *-*-cygwin* | *-*-mingw* | alpha*-dec-osf* )
       AC_DEFINE(GTHREAD_USE_WEAK, 0,
 		[Define to 0 if the target shouldn't use #pragma weak])
       ;;
diff --git a/libgfortran/configure.ac b/libgfortran/configure.ac
index 588f999..9b36103 100644
--- a/libgfortran/configure.ac
+++ b/libgfortran/configure.ac
@@ -491,14 +491,15 @@  LIBGFOR_CHECK_FLOAT128
 # Check for GNU libc feenableexcept
 AC_CHECK_LIB([m],[feenableexcept],[have_feenableexcept=yes AC_DEFINE([HAVE_FEENABLEEXCEPT],[1],[libm includes feenableexcept])])
 
-# At least for glibc, clock_gettime is in librt.  But don't pull that
-# in if it still doesn't give us the function we want.
-# This test is copied from libgomp, and modified to not link in -lrt
-# as libgfortran calls clock_gettime via a weak reference.
+# At least for glibc and Tru64, clock_gettime is in librt.  But don't
+# pull that in if it still doesn't give us the function we want.  This
+# test is copied from libgomp, and modified to not link in -lrt as
+# libgfortran calls clock_gettime via a weak reference if it's found
+# in librt.
 if test $ac_cv_func_clock_gettime = no; then
   AC_CHECK_LIB(rt, clock_gettime,
-    [AC_DEFINE(HAVE_CLOCK_GETTIME, 1,
-               [Define to 1 if you have the `clock_gettime' function.])])
+    [AC_DEFINE(HAVE_CLOCK_GETTIME_LIBRT, 1,
+               [Define to 1 if you have the `clock_gettime' function in librt.])])
 fi
 
 # Check for SysV fpsetmask
diff --git a/libgfortran/intrinsics/system_clock.c b/libgfortran/intrinsics/system_clock.c
index 3a44dd9..f4bac07 100644
--- a/libgfortran/intrinsics/system_clock.c
+++ b/libgfortran/intrinsics/system_clock.c
@@ -29,14 +29,16 @@  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 
 #include "time_1.h"
 
-#ifdef HAVE_CLOCK_GETTIME
+
 /* POSIX states that CLOCK_REALTIME must be present if clock_gettime
    is available, others are optional.  */
+#if defined(HAVE_CLOCK_GETTIME) || defined(HAVE_CLOCK_GETTIME_LIBRT)
 #ifdef CLOCK_MONOTONIC
 #define GF_CLOCK_MONOTONIC CLOCK_MONOTONIC
 #else
 #define GF_CLOCK_MONOTONIC CLOCK_REALTIME
 #endif
+#endif
 
 /* Weakref trickery for clock_gettime().  On Glibc, clock_gettime()
    requires us to link in librt, which also pulls in libpthread.  In
@@ -50,15 +52,9 @@  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define GTHREAD_USE_WEAK 1
 #endif
 
-#if SUPPORTS_WEAK && GTHREAD_USE_WEAK
+#if SUPPORTS_WEAK && GTHREAD_USE_WEAK && defined(HAVE_CLOCK_GETTIME_LIBRT)
 static int weak_gettime (clockid_t, struct timespec *) 
   __attribute__((__weakref__("clock_gettime")));
-#else
-static inline int weak_gettime (clockid_t clk_id, struct timespec *res)
-{
-  return clock_gettime (clk_id, res);
-}
-#endif
 #endif
 
 
@@ -84,6 +80,13 @@  gf_gettime_mono (time_t * secs, long * nanosecs)
 {
   int err;
 #ifdef HAVE_CLOCK_GETTIME
+  struct timespec ts;
+  err = clock_gettime (GF_CLOCK_MONOTONIC, &ts);
+  *secs = ts.tv_sec;
+  *nanosecs = ts.tv_nsec;
+  return err;
+#else
+#if defined(HAVE_CLOCK_GETTIME_LIBRT) && SUPPORTS_WEAK && GTHREAD_USE_WEAK
   if (weak_gettime)
     {
       struct timespec ts;
@@ -96,6 +99,7 @@  gf_gettime_mono (time_t * secs, long * nanosecs)
   err = gf_gettime (secs, nanosecs);
   *nanosecs *= 1000;
   return err;
+#endif
 }
 
 extern void system_clock_4 (GFC_INTEGER_4 *, GFC_INTEGER_4 *, GFC_INTEGER_4 *);