backport: re PR libstdc++/54847 (--enable-libstdcxx-time=yes doesn't find the functio...

backport: re PR libstdc++/54847 (--enable-libstdcxx-time=yes doesn't find the function nanosleep() on darwin)

2013-04-15  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.

From-SVN: r198003