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

[Samira Bazuzi via cfe-commits]

bazuzi wrote:

The fact that the code that revealed this bug was in a dataflow analysis isn't really relevant to the fix. I've added a unit test file with a new test limited only to the modified behavior of getFunctionType for BindingDecls.

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