This function has a single-value caching based on function local static variables.
This causes two problems:
* There is no synchronization, so this function randomly returns the demangled
name of other functions that are demangled at the same time.
* The 1-element cache is not very effective (the cache rate is around 0% when
running the LLDB test suite that calls this function around 30k times).
I would propose just removing it.
To prevent anyone else the git archeology: the static result variables were
originally added as this returned a ConstString reference, but that has since
been changed so that this returns by value.
Reviewed By: #lldb, JDevlieghere, shafik
Differential Revision: https://reviews.llvm.org/D103107
d28bc54ff4