[clang] [clang] Support -Wa, options -mmsa and -mno-msa (PR #99615)

[YunQiang Su via cfe-commits]

wzssyqa wrote:

> I figure out another use case:
> 
> ```
> f:
>         fadd.w  $w0,$w1,$w2
> ```
> 
>  ```
> # ./bin/clang --target=mipsel-linux-gnu -mfp64 -Wa,-mmsa -fintegrated-as -c xx.s 
> xx.s:2:2: error: instruction requires a CPU feature not currently enabled
>         fadd.w  $w0,$w1,$w2
>         ^
> ```
> 
>  ```
> # ./bin/clang --target=mipsel-linux-gnu -mfp64 -Wa,-mmsa -fno-integrated-as -c xx.s
> # Returns OK.
> ```
> 
> I guess that the use case of `-Wa,-mmsa` is to be compatible with some pre-exists software.

So I think that I want to know that which software asks for us to add such option?
As I understand, some software may set `AS` env as "CC -Wa,XXXX".  Is it?

https://github.com/llvm/llvm-project/pull/99615