[PatternRewriter] Disable copy/assign operators.

[lattner]

Summary

We had a bad bug over in CIRCT
caused by accidentally passing around PatternRewriter
by value. There is no reason to support copy/assignment
of the pattern rewriter, so disable it.

[lattner]

I committed this as "obvious", lemme know if you have any concerns and I'll revert.

[rriddle]

LG, thanks!

mlir/include/mlir/IR/PatternMatch.h

protected:
   /// hook into the reason why a rewrite failed, and display it to users.
   virtual LogicalResult
   notifyMatchFailure(Operation *op,
                      function_ref<void(Diagnostic &)> reasonCallback) {
     return failure();
   }
 
 private:
+  void operator=(const RewriterBase &) = delete;
+  RewriterBase(const RewriterBase &) = delete;
+
   /// 'op' and 'newOp' are known to have the same number of results, replace the
   /// uses of op with uses of newOp.
   void replaceOpWithResultsOfAnotherOp(Operation *op, Operation *newOp);
 };
 
 //===----------------------------------------------------------------------===//
 // IRRewriter
 //===----------------------------------------------------------------------===//