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

[YunQiang Su via llvm-commits]

wzssyqa wrote:

On My AARCH64 Mac
```
syq at syqs-iMac> clang --target=aarch64 -c xx.c                                                                                                                                                          
syq at syqs-iMac> file xx.o                                                                                                                                                                               
xx.o: ELF 64-bit LSB relocatable, ARM aarch64, version 1 (SYSV), not stripped
```

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