[clang] [clang] Function type attribute to prevent CFI instrumentation (PR #135836)

[Erich Keane via cfe-commits]

erichkeane wrote:

> @erichkeane We wanted C++ support so I tried adding exhaustive tests but I'm not sure if I caught everything. Would you be able to give a pass and see if I missed anything and what else should be tested? Also I'm having trouble coming up with a "struct redefinition" test. I think I'm misinterpreting N3037, but that looks like it has to do with type compatibility between different TUs rather than types within the same TU?

N3037 allows redefinition of the same struct within the same TU.  We only recently ahve an implementation of it (not sure if it has been merged yet).

I did a quick look, I didn't see anything about variable-type-aliases, static member functions, or explicit-this-type member functions, operators, etc.

https://github.com/llvm/llvm-project/pull/135836