The current implementation in AssembleSwap will generate a push-pop pair to swap between a general register and a stack slot for both x64 and ia32 targets. This is unnecessary for x64 target, as we can use the kScratchRegister to save the general register and swap with the stack slot.

Change-Id: I10e0dc360dec22cdf5afa63ece3d5943685d7ecb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2394177Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Yolanda Chen <yolanda.chen@intel.com>
Cr-Commit-Position: refs/heads/master@{#69726}