[llvm] [bolt][nfc] Fix test X86/dynamic-relocs-on-entry.s (PR #125264)

[Davide Italiano via llvm-commits]

https://github.com/dcci commented:

I see what's happening now. I think a better way of fixing this test would be that of using `llvm-readelf` rather than the system `readelf`.  This is used to dump parts of the executable, so the format isn't particularly relevant.

https://github.com/llvm/llvm-project/pull/125264