2013-04-12  Jack Howarth  <howarth@bromo.med.uc.edu>

	Backport from mainline

	2012-10-10  Jack Howarth  <howarth@bromo.med.uc.edu>
 		    Jonathan Wakely  <jwakely.gcc@gmail.com>

	PR libstdc++/54847
	* config/os/bsd/darwin/os_defines.h: Define _GLIBCXX_USE_NANOSLEEP
	and _GLIBCXX_USE_SCHED_YIELD.
	* acinclude.m4 (GLIBCXX_ENABLE_LIBSTDCXX_TIME): Add comment.

Index: libstdc++-v3/config/os/bsd/darwin/os_defines.h
===================================================================
--- libstdc++-v3/config/os/bsd/darwin/os_defines.h	(revision 197937)
+++ libstdc++-v3/config/os/bsd/darwin/os_defines.h	(working copy)
@@ -42,4 +42,9 @@
 // Static initializer macro is buggy in darwin, see libstdc++/51906
 #define _GTHREAD_USE_RECURSIVE_MUTEX_INIT_FUNC
 
+// Configure checks for nanosleep fail on Darwin, but nanosleep and
+// sched_yield are always available, so use them.
+#define _GLIBCXX_USE_NANOSLEEP 1
+#define _GLIBCXX_USE_SCHED_YIELD 1
+
 #endif
Index: libstdc++-v3/acinclude.m4
===================================================================
--- libstdc++-v3/acinclude.m4	(revision 197937)
+++ libstdc++-v3/acinclude.m4	(working copy)
@@ -1132,6 +1132,11 @@ dnl --enable-libstdcxx-time=no
 dnl --disable-libstdcxx-time
 dnl        disables the checks completely
 dnl
+dnl N.B. Darwin provides nanosleep but doesn't support the whole POSIX
+dnl Timers option, so doesn't define _POSIX_TIMERS. Because the test
+dnl below fails Darwin unconditionally defines _GLIBCXX_USE_NANOSLEEP in
+dnl os_defines.h and also defines _GLIBCXX_USE_SCHED_YIELD.
+dnl
 AC_DEFUN([GLIBCXX_ENABLE_LIBSTDCXX_TIME], [
 
   AC_MSG_CHECKING([for clock_gettime, nanosleep and sched_yield])