[lld] [ELF] Add support for PT_OPENBSD_NOBTCFI (PR #120005)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay commented:

I think this is fine... but it is not a good idea to keep introducing new PT_OPENBSD program headers...

https://github.com/llvm/llvm-project/pull/120005