testcase for my previous patch.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@56670 91177308-0d34-0410-b5e6-96231b3b80d8

test/Preprocessor/header_lookup1.c

@@ -0,0 +1,2 @@
+// RUN: clang -I /usr/include %s -E | grep 'stdio.h.*3.*4'
+#include <stdio.h>