[mlir] flush output in transform.print (#121382)

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.

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();
 }