CYGWIN seems to include _mingw.h and thus __MINGW64_VERSION_MAJOR is
defined even though rand_s is not available. Thus add an extra check
for __CYGWIN__.
2017-02-27 Janne Blomqvist <jb@gcc.gnu.org>
* intrinsics/random.c (getosrandom): Don't try to use rand_s on
CYGWIN.
From-SVN: r245755