[llvm] [DWARF] Fix DW_OP_LLVM_user sub-operation name lookup. (PR #217480)

[Eric Christopher via llvm-commits]

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

LGTM. @slinder1 asked for this to be split out so let's wait for their ack.

https://github.com/llvm/llvm-project/pull/217480