[clang] Return available function types for BindingDecls. (PR #102196)

[Samira Bazuzi via cfe-commits]

bazuzi wrote:

This is a pointer nullability analysis being developed outside of clang. The relevant analysis code, including our workaround, can be seen at https://github.com/google/crubit/blob/main/nullability/inference/collect_evidence.cc#L757.

https://github.com/llvm/llvm-project/pull/102196