[clang] [clang][PAC] Disallow -pedantic-errors in conjunction with pointer au… (PR #153503)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

I have prepared this PR as the only sound alternative to #153291 

While it will cause compilation failures for some projects, the alternative is incorrect codegen which is substantially worse.

https://github.com/llvm/llvm-project/pull/153503