[llvm] [IR] Add llvm.raw.sections named metadata (PR #226954)

[Steffen Larsen via llvm-commits]

steffenlarsen wrote:

Open question from https://github.com/llvm/llvm-project/pull/214135#issuecomment-5763065794:

> I do wonder if we need/want to support alloc sections via this mechanism at all, or limit it to non-alloc entirely.

It depends how much freedom we want. I lean towards adding the current degree of freedom for future extendibility, but cutting it to non-alloc would be more targetted the current use-case. I am not strongly tied to the current degree of freedom though.

https://github.com/llvm/llvm-project/pull/226954