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

[via llvm-commits]

https://github.com/jeffreytan81 commented:

Per my understanding, these two mutex are required to protect any read/write to DieArray field? If so, there seem to be many more accesses of this field not protected?

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