__atomic_test_and_set: Fall back to library, not non-atomic code

__atomic_test_and_set: Fall back to library, not non-atomic code

Make __atomic_test_and_set consistent with other __atomic_ and __sync_
builtins: call a matching library function instead of emitting
non-atomic code when the target has no direct insn support.

There's special-case code handling targetm.atomic_test_and_set_trueval
!= 1 trying a modified maybe_emit_sync_lock_test_and_set.  Previously,
if that worked but its matching emit_store_flag_force returned NULL,
we'd segfault later on.  Now that the caller handles NULL, gcc_assert
here instead.

While the referenced PR:s are ARM-specific, the issue is general.

	PR target/107567
	PR target/109166
	* builtins.cc (expand_builtin) <case BUILT_IN_ATOMIC_TEST_AND_SET>:
	Handle failure from expand_builtin_atomic_test_and_set.
	* optabs.cc (expand_atomic_test_and_set): When all attempts fail to
	generate atomic code through target support, return NULL
	instead of emitting non-atomic code.  Also, for code handling
	targetm.atomic_test_and_set_trueval != 1, gcc_assert result
	from calling emit_store_flag_force instead of returning NULL.