fix this test to fail when the patch isn't applied.

llvm-svn: 72385
diff --git a/clang/test/Preprocessor/assembler-with-cpp.c b/clang/test/Preprocessor/assembler-with-cpp.c
index bb16880..00080cc 100644
--- a/clang/test/Preprocessor/assembler-with-cpp.c
+++ b/clang/test/Preprocessor/assembler-with-cpp.c
@@ -64,7 +64,7 @@
 // RUN: grep 'T7 "foo"' %t &&
 
 // Concatenation with period doesn't leave a space
-// RUN: grep '.T8' %t &&
+// RUN: grep -F '.T8' %t &&
 #define T8(A,B) A ## B
 T8(.,T8)