libstdc++: Add wrapper for internal uses of std::terminate

This adds an inline wrapper for std::terminate that doesn't add the
declaration of std::terminate to namespace std. This allows the
library to terminate without including all of <exception>.

libstdc++-v3/ChangeLog:

	* include/bits/atomic_timed_wait.h: Remove unused header.
	* include/bits/c++config (std:__terminate): Define.
	* include/bits/semaphore_base.h: Remove <exception> and use
	__terminate instead of terminate.
	* include/bits/std_thread.h: Likewise.
	* libsupc++/eh_terminate.cc (std::terminate): Use qualified-id
	to call __cxxabiv1::__terminate.