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

[Fangrui Song via llvm-commits]

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@@ -0,0 +1,67 @@
+# REQUIRES: zlib
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MaskRay wrote:

Sounds good. Done. Added a zstd version.

There is `decompress-zlib-unsupported.test` but no `decompress-zstd-unsupported.test`. The latter probably doesn't add much coverage.

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