[clang] [llvm] [PowerPC] Diagnose musttail instead of crash inside backend (PR #93267)

[Matheus Izvekov via llvm-commits]

https://github.com/mizvekov approved this pull request.

Small nit, otherwise after you address @efriedma-quic 's concerns, this LGTM.

https://github.com/llvm/llvm-project/pull/93267