Use OpenBSD implementation for uv_fs_mkdtemp on Windows

As [stated](https://github.com/joyent/libuv/pull/1368/files#r15906993) by @sam-github libuv can't use glibc's modified code because glibc licensed under LGPL, but libuv under MIT. I apologize again, it was my fault because of ignorance.
So in this PR I ported [OpenBSD version](http://openbsd.cs.toronto.edu/cgi-bin/cvsweb/src/lib/libc/stdio/mktemp.c?rev=1.33&content-type=text/x-cvsweb-markup).
Main differences with original:
- `tries = TMP_MAX` instead of `tries = INT_MAX`. Though I'm not sure what is the best value.
- Used `rand` instead of `arc4random`. Though I found [portable arc4random.c](https://github.com/libevent/libevent/blob/master/arc4random.c) licensed under 3-clause BSD license. So it is possible to use it if appropriate.
I don't think that should be the responsibility of libuv.  Rather, I would add a note to the documentation for uv_fs_mkdtemp() that it's the responsibility of the libuv user to ensure that srand() has been called.

It's either that or:

1. Switch to a CSPRNG like CryptGenRandom(), or
2. Make the entropy the responsibility of the user, by means of a user-provided buffer or callback.

Option 1 makes the API easier to use but the user won't have much influence on the quality of the (CS)PRNG.

Option 2 makes the API more cumbersome but is useful in applications like node.js that have access to a cross-platform, high-quality entropy pool (OpenSSL's entropy pool in node's case.)

I don't have a preference, I'm just outlining the possibilities that I can think of.