[clang] [clang][Driver] Support -fms-volatile as equivalent to /volatile:ms (PR #74790)

[Reid Kleckner via cfe-commits]

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

> And it's a pretty straightforward extension to support (it just slightly modifies IR generation), so I don't think there's much long-term support burden.

I find that compelling, but make sure others' concerns are addressed.

https://github.com/llvm/llvm-project/pull/74790