Distinguish the various kinds of AST file loading failures:

file corruption, compiler version mismatch, target/language
configuration mismatch, out-of-date AST file. No functionality change
yet.

llvm-svn: 166446

clang/lib/Frontend/ChainedIncludesSource.cpp

@@ -46,7 +46,10 @@ static ASTReader *createASTReader(CompilerInstance &CI,
     return Reader.take();
 
   case ASTReader::Failure:
-  case ASTReader::IgnorePCH:
+  case ASTReader::OutOfDate:
+  case ASTReader::VersionMismatch:
+  case ASTReader::ConfigurationMismatch:
+  case ASTReader::HadErrors:
     break;
   }
   return 0;