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__.

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

libgfortran/ChangeLog

+2017-02-27  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	* intrinsics/random.c (getosrandom): Don't try to use rand_s on
+	CYGWIN.
+
 2017-02-16  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/79382

libgfortran/intrinsics/random.c

@@ -304,7 +304,7 @@ static int
 getosrandom (void *buf, size_t buflen)
 {
   /* rand_s is available in MinGW-w64 but not plain MinGW.  */
-#ifdef __MINGW64_VERSION_MAJOR
+#if defined(__MINGW64_VERSION_MAJOR) && !defined(__CYGWIN__)
   unsigned int* b = buf;
   for (unsigned i = 0; i < buflen / sizeof (unsigned int); i++)
     rand_s (&b[i]);