Debug build needs more scratch registers, since s0 is not added to
allocatable registers, we could use it as a scratch register.

Change-Id: I1453d78b18cd3abff83a2f0c084ed4dd92e92884
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3313967Reviewed-by: Liu yu <liuyu@loongson.cn>
Commit-Queue: Liu yu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/main@{#78225}