[llvm] [llvm-symbolizer] nfc, use map instead of vector (PR #69552)

[James Henderson via llvm-commits]

https://github.com/jh7370 requested changes to this pull request.

As an additional note, I see your subsequent change is to support some XCOFF functionality. I'd be strongly opposed to making performance worse for all output types, just to support some additional XCOFF functionality, so I'm specifically marking with "Request changes" until you've provided some profile information for ELF and perhaps other output formats.

https://github.com/llvm/llvm-project/pull/69552