Speculative fix 2 for Clang ToT bots after upstream r332021

Add a missing 'clang::' namespace qualifier.

TBR=thakis@chromium.org
NOTRY=True
BUG=841908

Change-Id: I60e48efbfd92017a3802e9f74d77a9ddcb307b27
Reviewed-on: https://chromium-review.googlesource.com/1054527Reviewed-by: Reid Kleckner <rnk@chromium.org>
Commit-Queue: Reid Kleckner <rnk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557670}

tools/clang/translation_unit/TranslationUnitGenerator.cpp

@@ -63,7 +63,7 @@ class IncludeFinderPPCallbacks : public clang::PPCallbacks {
                           const clang::Module* imported
 #if defined(LLVM_FORCE_HEAD_REVISION)
                           ,
-                          SrcMgr::CharacteristicKind /*file_type*/
+                          clang::SrcMgr::CharacteristicKind /*file_type*/
 #endif
                           ) override;
   void EndOfMainFile() override;
@@ -151,7 +151,7 @@ void IncludeFinderPPCallbacks::InclusionDirective(
     const clang::Module* imported
 #if defined(LLVM_FORCE_HEAD_REVISION)
     ,
-    SrcMgr::CharacteristicKind /*file_type*/
+    clang::SrcMgr::CharacteristicKind /*file_type*/
 #endif
     ) {
   if (!file)