[PAC][libunwind] Enhance comments and error messages related to libunwind hardening

[kovdan01]

#143230 introduces libunwind hardening which could be used with pauth-enabled ABIs (such as arm64e for Apple and pauthtest for Linux). However, since the hardening was initially implemented for Apple's arm64e, several comments and messages mention that instead of generic pauth terms.

These messages should be re-phrased so they are applicable for pauthtest and other potential pauth-enabled ABIs as well.

See, for example, #143230 (comment)

[kovdan01]

Tagging @asl @ojhunt @atrosinenko