[clang] [Frontend][Sema] Add CC1-only -fms-anonymous-structs to enable Microsoft anonymous struct/union feature (PR #176551)

[Riyaz Ahmad via cfe-commits]

riyaz86a wrote:

> One other change we should make is to document the extension explicitly in clang/docs/LanguageExtensions.rst so users know about the functionality.
Missed to handle this, will take care of it.


https://github.com/llvm/llvm-project/pull/176551