message: handleDiagnostic gets default loc, not filename.
diff: @@ -2733,7 +2733,7 @@ public:
  llvm::StringRef formatString,
  llvm::ArrayRef<swift::DiagnosticArgument> formatArgs,
  const swift::DiagnosticInfo &info,
  - StringRef currentPrimaryInput) {
  + const SourceLoc defaultDiagnosticLoc) {
  llvm::StringRef bufferName = "<anonymous>";
  unsigned bufferID = 0;
  std::pair<unsigned, unsigned> line_col = {0, 0};
  