Due to MIPS64 ISA feature, 32-bit values should be sign-extended
in 64-bit registers, no matter it's signed or unsigned.

Besides, LoongArch64 also has this feature, and a similar change
has been made before loong64 port's land in V8. This CL also make
a small fix for loong64.

Change-Id: Ib284662931082365f727925af61781e3653debc8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3193595Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Liu yu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/main@{#77154}