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

[Greg Clayton via llvm-commits]

================
@@ -257,6 +258,9 @@ class DWARFUnit {
 
   std::shared_ptr<DWARFUnit> DWO;
 
+  mutable llvm::sys::RWMutex m_cu_die_array_mutex;
----------------
clayborg wrote:

LLDB coding guidelines are a bit different for instance variables: to don't prefix with `m_` and they use camel case. So this should be something like:
```
mutable llvm::sys::RWMutex  CUDieArrayMutex;
```

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