[llvm] [MC] Replace MCContext::GenericSectionID with MCSection::NonUniqueID (PR #126202)

[Alexis Engelke via llvm-commits]

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

History: 97837b7b091621537854a753942ce504560dee45 (2016) added support for unique IDs in sections and added `GenericSectionID`. Later, 1dc16c752dd3dcd41ed320c2ea7647ea5bd7736e (2020/@MaskRay) added `NonUniqueID`.

I agree that MCSection::NonUniqueID is nicer and the more logical place; it also avoids pulling in MCContext.h into MCSectionELF.h.

LGTM (unless @MaskRay has concerns).

https://github.com/llvm/llvm-project/pull/126202