libstdc++: Restore std::scoped_lock for non-gthreads targets [PR120198]

libstdc++: Restore std::scoped_lock for non-gthreads targets [PR120198]

This was a regression introduced with using version.def to define
feature test macros (r14-3248-g083b7f2833d71d). std::scoped_lock doesn't
need to depend on gthreads and so can be defined unconditionally, even
for freestanding.

libstdc++-v3/ChangeLog:

	PR libstdc++/120198
	* include/bits/version.def (scoped_lock): Do not depend on
	gthreads or hosted.
	* include/bits/version.h: Regenerate.
	* include/std/mutex (scoped_lock): Update comment.
	* testsuite/30_threads/scoped_lock/requirements/typedefs.cc:
	Remove dg-require-gthreads and use custom lockable type instead
	of std::mutex. Check that typedef is only present for a single
	template argument.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>