[lld] [llvm] [Object][ELF] Support extended header for Object Parser in ELF (PR #162288)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Please remove the lld/ELF change. For linker output we don't intend to support the PN_XNUM program header feature. We also don't accept features without a test.

Link: https://groups.google.com/g/generic-abi/c/-J3lNY8ZKkU ("PN_XNUM extension for program headers")

https://github.com/llvm/llvm-project/pull/162288