[tests] Add a test for -iwithprefix.

- This just scratches the surface, We have pretty horrible test coverage in
   this area it seems like, but this at least covers the change in r173410.

llvm-svn: 173464

clang/test/Preprocessor/iwithprefix.c

@@ -0,0 +1,16 @@
+// Check that -iwithprefix falls into the "after" search list.
+//
+// RUN: rm -rf %t.tmps
+// RUN: mkdir -p %t.tmps/first %t.tmps/second
+// RUN: %clang_cc1 \
+// RUN:   -iprefix %t.tmps/ -iwithprefix second \
+// RUN:    -isystem %t.tmps/first -v 2> %t.out
+// RUN: FileCheck < %t.out %s
+
+// CHECK: #include <...> search starts here:
+// CHECK: {{.*}}.tmps/first
+// CHECK: /usr/include
+// CHECK: {{.*}}.tmps/second
+// CHECK-NOT: {{.*}}.tmps
+
+