re PR libstdc++/51296 (Several 30_threads tests FAIL on Tru64 UNIX)

re PR libstdc++/51296 (Several 30_threads tests FAIL on Tru64 UNIX)

libgcc/

	PR libstdc++/51296
	PR libstdc++/51906
	* gthr-posix.h: Allow static initializer macros to be disabled.
	(__gthrw_pthread_cond_init): Define weak reference unconditionally.

libstdc++-v3/

	PR libstdc++/51296
	* include/std/mutex (__mutex_base::~__mutex_base): Declare noexcept.
	* src/c++11/condition_variable.cc (condition_variable): Use macro for
	initializer function.

	PR libstdc++/51906
	* config/os/bsd/darwin/os_defines.h: Disable static initializer for
	recursive mutexes.

From-SVN: r183955