[clang] Try to unbreak test/C/drs/dr324.c on Windows

The test uses

    #pragma GCC dependency "oops\..\dr0xx.c"

to test preprocessor "tokenization obscurities". However, that
pragma also emits a warning if the refered file is newer than the
current file -- and d694e24 edited dr0xx.c, causing this warning
to fire.

As workaround, touch this file, so that it's newer than dr0xx.c again.

Author: nico

clang/test/C/drs/dr324.c

@@ -21,7 +21,7 @@ char lit_char = '\y';       /* expected-warning {{unknown escape sequence '\y'}}
  * The second pragma is a string-literal and so the \d is invalid there.
  */
 #ifdef _WIN32
-/* This test only makes sense on Windows targets where the backslash is a valid
+/* This test only makes sense on Windows targets, where the backslash is a valid
  * path separator.
  */
 #pragma GCC dependency "oops\..\dr0xx.c"