[llvm] [symbolizer] Support symbol+offset lookup (PR #75067)

[James Henderson via llvm-commits]

https://github.com/jh7370 approved this pull request.

LGTM, with nits.

I asked in the Phabricator review whether GNU allows negative offsets. If it does, that functionality can be added in a follow-up patch.

https://github.com/llvm/llvm-project/pull/75067