[clang] [SPARC][Driver] Move feature mode selection to Arch/Sparc.cpp (PR #149652)

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koachan wrote:

> > This is so that it's performed globally and not just for clang.
> 
> Can you elaborate what is "globally"?

Ah, I meant for flang and other frontends too, not just clang, as per the bug report [here](https://github.com/llvm/llvm-project/issues/138494).

https://github.com/llvm/llvm-project/pull/149652