[lld] [ELF] Reject certain unknown section types (PR #85173)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Thanks for the additional context. My motivation was primarily to detect new section types in the generic range `[0, SHT_LOOS)`. These new generic section types, if introduced, may be about new control structures that replace the existing, size-inefficient ones, e.g. https://discourse.llvm.org/t/rfc-relleb-a-compact-relocation-format-for-elf/77600 

I agree that we can optionally tighten up the processor specific section in a follow up patch.

I think certain architectures probably don't want the old-linker-detecting behavior ("time travel compatibility"). So we might not want to introduce the behavior.

https://github.com/llvm/llvm-project/pull/85173