PR middle-end/51038

	libstdc++-v3
	* include/bits/atomic_base.h (atomic_thread_fence): Call built-in.
	(atomic_signal_fence): Call built-in.
	(test_and_set, clear): Call new atomic built-ins.

	gcc
	* builtins.c (expand_builtin_atomic_clear): New.  Expand atomic_clear.
	(expand_builtin_atomic_test_and_set): New.  Expand atomic test_and_set.
	(expand_builtin): Add cases for test_and_set and clear.
	* sync-builtins.def (BUILT_IN_ATOMIC_TEST_AND_SET): New.
	(BUILT_IN_ATOMIC_CLEAR): New.

	testsuite
	* gcc.dg/atomic-invalid.c: Add test for invalid __atomic_clear models.
	* gcc.dg/atomic-flag.c: New.  Test __atomic_test_and_set and
	__atomic_clear.

From-SVN: r181271