message: Support parsing MLIR source from stdin.
diff: @@ -4166,7 +4166,7 @@ Module *mlir::parseSourceFile(StringRef filename, llvm::SourceMgr &sourceMgr,
  "only main buffer parsed at the moment");
  return nullptr;
  }
  - auto file_or_err = llvm::MemoryBuffer::getFile(filename);
  + auto file_or_err = llvm::MemoryBuffer::getFileOrSTDIN(filename);
  if (std::error_code error = file_or_err.getError()) {
  emitError(mlir::UnknownLoc::get(context),
  "could not open input file " + filename);
  