[llvm] [llvm-readobj,ELF] Support --decompress/-z (PR #82594)

[Ed Maste via llvm-commits]

https://github.com/emaste approved this pull request.

Thanks!

For an unsupported case I thought you might have a non-zlib/zstd case, 
```
...
    Flags: [SHF_COMPRESSED]
    Content: 03.....
```

https://github.com/llvm/llvm-project/pull/82594