[clang] Split -Wcast-function-type into a separate group (PR #86131)

[Abhin P Jose via cfe-commits]

Abhinkop wrote:

Yes, I will create a separate patch. I'm not sure it would be able to do it in this patch. I am halfway through verifying the fix in this patch.

https://github.com/llvm/llvm-project/pull/86131