test: fix test-fs-file-loop on Windows
test: fix test-fs-file-loop on Windows

* Check whether uv_fs_symlink() succeeds.
* Bail out early if we're on an old version of windows, or if we're not
  able to create symlinks because we're not elevated.

PR-URL: https://github.com/libuv/libuv/pull/55
Reviewed-By: Saúl Ibarra Corretgé <8a7991f6950ea189abf159d6ec98d2fcc13dc5f6@gmail.com>

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