[llvm] [MIPS] Sign-extend subwords when expanding atomic max/min (PR #89246)

[YunQiang Su via llvm-commits]

wzssyqa wrote:

[test_max_16.s.gz](https://github.com/llvm/llvm-project/files/15042191/test_max_16.s.gz)

Maybe this asm code is helpful.

https://github.com/llvm/llvm-project/pull/89246