test/Modules/compiler_builtins.m: Appease Cygwin to add -D__need_wint_t.

On Cygwin, at first, <stddef.h> is included without __need_wint_t.
Next, <stddef.h> is included with __need_wint_t, though Modules feature would not process <stddef.h> twice.
Then, wint_t is not found in system headers.

llvm-svn: 149500

clang/test/Modules/compiler_builtins.m

@@ -1,5 +1,5 @@
 // RUN: rm -rf %t
-// RUN: %clang -fsyntax-only -fmodules -fmodule-cache-path %t %s -Xclang -verify
+// RUN: %clang -fsyntax-only -fmodules -fmodule-cache-path %t -D__need_wint_t %s -Xclang -verify
 
 @import _Builtin_stdlib.float_constants;