Fix sign error in SYSTEM_CLOCK kind=4 Windows version.

2013-04-28  Janne Blomqvist  <jb@gcc.gnu.org>

	* intrinsics/system_clock.c (system_clock_4): Fix sign error in
	Windows version.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@198378 138bc75d-0d04-0410-961f-82ee72b054a4