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

[Oliver Hunt via cfe-commits]

ojhunt wrote:

<please hold while I update this PR to some notion of today's tree - I forgot I had been hunting a regression earlier and wrote this on top of a very old tree>

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