Revert "Modules: Make missing headers in a module.map a warning not an error."

This was committed accidentally.

llvm-svn: 197389
diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index 254c029..5770aaa 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -48,7 +48,7 @@
                            const LangOptions &LangOpts, 
                            const TargetInfo *Target)
   : HSOpts(HSOpts), FileMgr(SourceMgr.getFileManager()), FrameworkMap(64),
-    ModMap(SourceMgr, Diags, LangOpts, Target, *this)
+    ModMap(SourceMgr, *Diags.getClient(), LangOpts, Target, *this)
 {
   AngledDirIdx = 0;
   SystemDirIdx = 0;