[libunwind] [libunwind] introduce _LIBUNWIND_TRACE_DWARF_EVAL for increased baremetal friendliness (PR #72040)

[Alexander Richardson via cfe-commits]

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

I'm happy with this as is but I'd wait for at least one other positive review before merging.

https://github.com/llvm/llvm-project/pull/72040