[Patch, libgfortran, committed] Don't use rand_s on CYGWIN

[Janne Blomqvist]

Don't try to use rand_s on CYGWIN

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__.

Thanks to Tim Prince and Nightstrike for bringing this issue to my attention.

Committed as r245755.

2017-02-27  Janne Blomqvist  <jb@gcc.gnu.org>

    * intrinsics/random.c (getosrandom): Don't try to use rand_s on
    CYGWIN.


-- 
Janne Blomqvist