[llvm] [llvm-nm] Fix heap-use-after-free while executing 'llvm-nm -n --export-symbols' (PR #65668)

[Fangrui Song via llvm-commits]

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

Since this is purely code simplification, I think this is fine.

https://github.com/llvm/llvm-project/pull/65668