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

[Abhin P Jose via cfe-commits]

Abhinkop wrote:

I think that this would occur primarily in the whole code base. Because a compilation that has added -Wextra diagnostic group would provide new warnings and coupling, this with -Werror would break the build. I think we have to take a look at these builds and investigate why it is done, and for the time being, we can use the -Wno-cast-function-type to make the builds go green.

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