[llvm] [CodeGen][Mips] Explicit ELF output file format for MIPS tests (PR #114678)

[YunQiang Su via llvm-commits]

wzssyqa wrote:

LLVM doesn't expect that the behavior of same command has different behaviors on different platforms.

Aka, you should always use something like `--triple=mips-coff` if you need the object to be a COFF.

https://github.com/llvm/llvm-project/pull/114678