unix: don't copy arguments for sync fs requests
unix: don't copy arguments for sync fs requests

For synchronous file operation requests (ones without a callback), there
is no need to make a copy of the arguments because they don't outlive
the scope of the function call.

PR-URL: https://github.com/libuv/libuv/pull/479
Reviewed-By: Saúl Ibarra Corretgé <8a7991f6950ea189abf159d6ec98d2fcc13dc5f6@gmail.com>

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso