[builtins][x64] Save an instruction by doing the Tagging in-place

If we SmiTag using the same register we will save a mov instruction.

Bug: v8:9771
Change-Id: Iadfa332e76115688eac6c3ec5262ca751ec02405
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1826735Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64029}

src/builtins/x64/builtins-x64.cc

@@ -1455,8 +1455,9 @@ void Builtins::Generate_InterpreterEnterBytecodeAdvance(MacroAssembler* masm) {
                                 &if_return);
 
   // Convert new bytecode offset to a Smi and save in the stackframe.
-  __ SmiTag(rbx, kInterpreterBytecodeOffsetRegister);
-  __ movq(Operand(rbp, InterpreterFrameConstants::kBytecodeOffsetFromFp), rbx);
+  __ SmiTag(kInterpreterBytecodeOffsetRegister);
+  __ movq(Operand(rbp, InterpreterFrameConstants::kBytecodeOffsetFromFp),
+          kInterpreterBytecodeOffsetRegister);
 
   Generate_InterpreterEnterBytecode(masm);