[llvm] Fix compression header size check in ELF writer (PR #66888)

[via llvm-commits]

zmodem wrote:

As it turns out, this breaks at least two lit tests when building with `-DLLVM_ENABLE_ZSTD=ON` enabled:

```
 Failed Tests (2):
   Clang :: Misc/cc1as-compress.s
   LLVM :: MC/ELF/compress-debug-sections-zstd.s
```

(See https://bugs.chromium.org/p/chromium/issues/detail?id=1499858)

Probably the expectations just need updating, and then we'd have this tested :-)

I'll revert it for now to unbreak the builds.

https://github.com/llvm/llvm-project/pull/66888