Unify implementations of __builtin_mem_*_fence and __sync_synchronize.

Unify implementations of __builtin_mem_*_fence and __sync_synchronize.

	* builtins.c (expand_builtin_mem_thread_fence): Remove.
	(expand_builtin_mem_signal_fence): Remove.
	(expand_builtin_atomic_thread_fence): Use expand_mem_thread_fence.
	(expand_builtin_sync_synchronize): Likewise.
	(expand_builtin_atomic_signal_fence): Use expand_mem_signal_fence.
	* optabs.c (expand_asm_memory_barrier): Split out from
	expand_builtin_mem_signal_fence.
	(expand_mem_thread_fence): New, a combination of code from
	expand_builtin_mem_thread_fence and expand_builtin_sync_synchronize.
	(expand_mem_signal_fence): Moved and renamed from
	expand_builtin_mem_signal_fence.
	(expand_atomic_exchange): Use expand_mem_thread_fence.
	(expand_atomic_load, expand_atomic_store): Likewise.
	* expr.h, optabs.h: Update decls.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@181451 138bc75d-0d04-0410-961f-82ee72b054a4