Add fake-use for variable in LLVMDialect.cpp to fix opt build.

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PiperOrigin-RevId: 241620442

mlir/lib/LLVMIR/IR/LLVMDialect.cpp

@@ -66,6 +66,7 @@ static void printLLVMBinaryOp(OpAsmPrinter *p, Operation *op) {
   // Fallback to the generic form if the op is not well-formed (may happen
   // during incomplete rewrites, and used for debugging).
   const auto *abstract = op->getAbstractOperation();
+  (void)abstract;
   assert(abstract && "pretty printing an unregistered operation");
 
   auto resultType = op->getResult(0)->getType();