[llvm] [MC][ELF] Eliminate some hash maps from ELFObjectWriter (PR #97421)

[Alexis Engelke via llvm-commits]

aengelke wrote:

> but the indirection might harm performance.

Agreed that the space savings are likely to hurt performance. Would be nice to remove the 60 padding bits from MCSymbol, though.

> Group signature symbols are strange

Yes, I also learned that while working on this...

Thanks for the review and comments!

https://github.com/llvm/llvm-project/pull/97421