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

[Amy Kwan via cfe-commits]

amy-kwan wrote:

Thanks @Abhinkop for the patch! I have approved the compiler-rt patch since it does appear to resolve the check-runtimes/check-all issue for the asan test case.

If you also would like me to test a follow up patch for `llvm-project/llvm/lib/IR/Core.cpp`, I would be happy to do so, as well.

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