[clang] Diagnose problematic uses of constructor/destructor attribute (PR #67360)

[Nick Desaulniers via cfe-commits]

nickdesaulniers wrote:

ah, yeah I was curious about what precisely `reserved for the implementation` meant. System libraries? That means they should be able to opt out via `-Wno-whatever`.

For anything thats */test/*, I assume they can be adjusted to just not use a reserved priority?

https://github.com/llvm/llvm-project/pull/67360