[llvm-branch-commits] [llvm-objcopy] Simplify --[de]compress-debug-sections and don't compress SHF_ALLOC sections (PR #84885)

[Fangrui Song via llvm-branch-commits]

https://github.com/MaskRay created https://github.com/llvm/llvm-project/pull/84885

Make it easier to add custom section [de]compression. In GNU ld,
--compress-debug-sections doesn't compress SHF_ALLOC sections. Match its
behavior.