[llvm] Reduce llvm-gsymutil memory usage (PR #91023)

[Alexander Yermolovich via llvm-commits]

ayermolo wrote:

OK. I think this two lock thing makes sense in my head.
One concern I have is that between locks in tryExtractDIEsIfNeeded it switches to clearDIEs.


https://github.com/llvm/llvm-project/pull/91023