[compiler-rt] [libcxxabi] [libunwind] [runtimes][PAC] Harden unwinding when possible (#138571) (PR #143230)

[Oliver Hunt via llvm-commits]

ojhunt wrote:

Build failures are due to me applying some review feedback and then completely failing to actually verify things still built. #Skilled

https://github.com/llvm/llvm-project/pull/143230