helper/options: Add missing #include for MinGW and MSYS2

Change-Id: I3bb295f52706b641661241e3e047306811ca915e
Signed-off-by: Marc Schink <openocd-dev@marcschink.de>
Reviewed-on: http://openocd.zylin.com/4201
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/helper/options.c

@@ -37,6 +37,9 @@
 #ifdef HAVE_SYS_SYSCTL_H
 #include <sys/sysctl.h>
 #endif
+#if IS_WIN32 && !IS_CYGWIN
+#include <windows.h>
+#endif
 
 static int help_flag, version_flag;