re PR libstdc++/56002 ([C++11] allow generic locks to be used without requiring plattform support for threads)

	PR libstdc++/56002
	* include/std/mutex (lock_guard, unique_lock, lock): Define without
	depending on _GLIBCXX_HAS_GTHREADS.
	* testsuite/30_threads/lock_guard/cons/1.cc: Run on all targets.

From-SVN: r196706