[llvm] Two DWARF variant part improvements (PR #138953)

[Tom Tromey via llvm-commits]

tromey wrote:

> The newly added test file is failing on the AIX buildbot. @tromey, can you please take a look? https://lab.llvm.org/buildbot/#/builders/64/builds/3465/steps/6/logs/FAIL__LLVM__discriminant-member_ll

I'll look at it today.  Sorry about the breakage.

https://github.com/llvm/llvm-project/pull/138953