[mlir] flush output in transform.print

Print operations are often used for debugging, immediately before the compiler
aborts. In such cases, it is sometimes possible that the output isn't fully
produced yet. Make sure it is by explicitly flushing the output.

Author: ftynse

mlir/lib/Dialect/Transform/IR/TransformOps.cpp

@@ -2840,6 +2840,7 @@ transform::PrintOp::apply(transform::TransformRewriter &rewriter,
     llvm::outs() << "top-level ]]]\n";
     state.getTopLevel()->print(llvm::outs(), printFlags);
     llvm::outs() << "\n";
+    llvm::outs().flush();
     return DiagnosedSilenceableFailure::success();
   }
 
@@ -2849,6 +2850,7 @@ transform::PrintOp::apply(transform::TransformRewriter &rewriter,
     llvm::outs() << "\n";
   }
 
+  llvm::outs().flush();
   return DiagnosedSilenceableFailure::success();
 }