Don't use Win32 functions on CYGWIN.

This was a workaround for a cygwin bug which was fixed 4 years ago,
and cygwin hasn't supported affected versions for a long time.

2017-03-15  NightStrike  <nightstrike@gmail.com>
	    Janne Blomqvist  <jb@gcc.gnu.org>

	* intrinsics/random.c (getosrandom): Remove check for __CYGWIN__
	preprocessor flag.
	* intrinsics/system_clock.c: Likewise.
	(system_clock_4): Likewise.
	(system_clock_8): Likewise.
	* intrinsics/time_1.h: Don't include windows.h if __CYGWIN__ is
	defined.

Co-Authored-By: Janne Blomqvist <jb@gcc.gnu.org>

From-SVN: r246162