[libcxxabi] [llvm] Fix C++ demangling for _BitInt type (PR #143466)

[Larry Meadows via llvm-commits]

lfmeadow wrote:

@ldionne Are you satisfied with my response, or do you need me to try to figure out when/where clang started producing these manglings? 

https://github.com/llvm/llvm-project/pull/143466