[clang] [SFrame][Retry] Add assembler option --gsframe (PR #165806)

[Tarun Prabhu via cfe-commits]

https://github.com/tarunprabhu approved this pull request.

Barring the slight tweak to the help message, this LGTM. 

However, I primarily work on `flang`, so I have requested a review from @MaskRay since this is primarily `clang`. Please wait for approval from @MaskRay as well before merging. 

Thanks!

https://github.com/llvm/llvm-project/pull/165806