Make the difference between cfg(target_os = "macos") and cfg(not(target_os = "linux")) clearer

[liubin]

There are two types of checking different OSs:

ttrpc-rust/src/sync/server.rs

Lines 335 to 341 in 212d221

	#[cfg(not(target_os = "linux"))]
	let fds = {
	let (rfd, wfd) = pipe()?;
	set_fd_close_exec(rfd)?;
	set_fd_close_exec(wfd)?;
	(rfd, wfd)
	};

ttrpc-rust/src/common.rs

Lines 120 to 123 in dfae1ad

	// MacOS doesn't support atomic creation of a socket descriptor with SOCK_CLOEXEC flag,
	// so there is a chance of leak if fork + exec happens in between of these calls.
	#[cfg(target_os = "macos")]
	set_fd_close_exec(fd)?;

Should these use the consistent way, for example, the pairs of:

• target_os = "linux" and target_os = "macos"
• target_os = "linux" and not(target_os = "linux")

[mxpv]

I think this partially intersects with #132
SOCK_CLOEXEC fix applicable to both windows and mac os, so it make sense to use not(linux) or any(windows, macos).