Fine-tune the Ordering for the atomic usages

[wang384670111]

SeqCst is overly restrictive. I believe that the ordering can be appropriately modified.
I think that USE_ERRORMODE is merely signal for multithreading purposes and do not synchronize with other locals. Therefore, using Relaxed ordering should suffice.

rust-dlopen/src/raw/windows.rs

Lines 68 to 79 in f9fed71

	if !USE_ERRORMODE.load(Ordering::Acquire) {
	let mut previous: DWORD = 0;
	if unsafe { SetThreadErrorMode(ERROR_MODE, &mut previous) } == 0 {
	//error. On some systems SetThreadErrorMode may not be implemented
	let error = unsafe { GetLastError() };
	if error == ERROR_CALL_NOT_IMPLEMENTED {
	USE_ERRORMODE.store(true, Ordering::Release);
	} else {
	//this is an actual error
	//SetErrorMode never fails. Shouldn't we use it now?
	return Err(IoError::from_raw_os_error(error as i32));
	}