[clang] [PAC][clang] Use `Error` behavior for ptrauth module flags (PR #189923)

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

I'm not very familiar with managing the module flags, but this sounds reasonable, thanks.

Aside from obvious reason to **sign** the GOT entries, Clang's documentation on Pointer Authentication [mentions](https://clang.llvm.org/docs/PointerAuthentication.html#global-offset-tables) that there are valid reasons **against** signing GOT entries when RELRO is absolutely known to be in effect. Given that, erroring out on any disagreement seems to be the safest option.

Considering `ptrauth-sign-personality`, even Max should be acceptable, I guess, but Error is of course the safest by default.

Do I get it right these discrepancies are not expected in a properly set up environment?

https://github.com/llvm/llvm-project/pull/189923