Don't run Gnu.C test on Windows...

Author: bellenot

test/Driver/Gnu.C

@@ -10,6 +10,7 @@
 // RUN: cat %s | %cling -D__STRICT_ANSI__ -std=gnu++11 -Xclang -verify 2>&1 | FileCheck %s
 // RUN: cat %s | %cling -D__STRICT_ANSI__ -std=gnu++14 -Xclang -verify 2>&1 | FileCheck %s
 // RUN: cat %s | %cling -D__STRICT_ANSI__ -std=gnu++1z -Xclang -verify 2>&1 | FileCheck %s
+// REQUIRES: not_system-windows
 
 #ifdef __cplusplus
 extern "C" int printf(const char*, ...);