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

[via cfe-commits]

yingopq wrote:




> > I figure out another use case:
> > ```
> > f:
> >         fadd.w  $w0,$w1,$w2
> > ```
> > 
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> > ```
> > # ./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
> >        ^
> > ```
> > 
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> > ```
> > # ./bin/clang --target=mipsel-linux-gnu -mfp64 -Wa,-mmsa -fno-integrated-as -c xx.s
> > # Returns OK.
> > ```
> > 
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> > 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?

This is a required task @FlyGoat mentioned before.

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