[clang] [clang] Support member function poiners in Decl::getFunctionType() (PR #125077)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic approved this pull request.

LGTM... but I have a couple comments on things you mentioned in the commit message.

> ```
> /// Looks through the Decl's underlying type to extract a FunctionType
> /// when possible. Will return null if the type underlying the Decl does not
> /// have a FunctionType.
>```

Maybe the description here should more explicitly state that it looks for function pointers as well as functions...

> error: '<attr>' only applies to non-K&R-style functions

Probably we should fix the error message not to mention K&R unless we actually find a K&R-style function type.

https://github.com/llvm/llvm-project/pull/125077