Clang: Make use of CXTranslationUnit_KeepGoing

From the documentation:

 Do not stop processing when fatal errors are encountered.

 When fatal errors are encountered while parsing a translation unit,
 semantic analysis is typically stopped early when compiling code. A common
 source for fatal errors are unresolvable include files. For the
 purposes of an IDE, this is undesirable behavior and as much information
 as possible should be reported. Use this flag to enable this behavior.

Change-Id: I0af9f7b1ed68c41e9bcf0abf97d8a4e22dc124ca
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/tools/clangbackend/ipcsource/clangtranslationunitupdater.cpp

@@ -176,7 +176,8 @@ uint TranslationUnitUpdater::defaultParseOptions()
     return CXTranslationUnit_CacheCompletionResults
          | CXTranslationUnit_PrecompiledPreamble
          | CXTranslationUnit_IncludeBriefCommentsInCodeCompletion
-         | CXTranslationUnit_DetailedPreprocessingRecord;
+         | CXTranslationUnit_DetailedPreprocessingRecord
+         | CXTranslationUnit_KeepGoing;
 }
 
 void TranslationUnitUpdater::createIndexIfNeeded()