fix PR3798 by ignoring all diagnostics generated while repreprocessing a file in rewrite macros.

llvm-svn: 66961
diff --git a/clang/test/Misc/emit-html.c b/clang/test/Misc/emit-html.c
index c4a1845..8c6556e 100644
--- a/clang/test/Misc/emit-html.c
+++ b/clang/test/Misc/emit-html.c
@@ -9,3 +9,10 @@
   return F(argc, 1);
 }
 
+// PR3798
+#define FOR_ALL_FILES(f,i) i
+
+#if 0
+  FOR_ALL_FILES(f) { }
+#endif
+