Add a working Windows tmpfile(3) to fastboot.

Windows' tmpfile(3) implementation requires administrator rights because
it creates temporary files in the root directory. Write an alternative
that uses the user's temporary directory instead.

Bug: http://b/21558406
Change-Id: Ic9aece5c69429797a332a97681a76b76ac3551bf
(cherry picked from commit a26fbeea)