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

[Peter Dimov via cfe-commits]

pdimov wrote:

The above was a 64 bit build, in 32 bit the warning is
```
1>testbed2022.cpp(8,15): warning : cast from 'FARPROC' (aka 'int (*)() __attribute__((stdcall))') to 'PGNSI' (aka 'void (*)(_SYSTEM_INFO *) __attribute__((stdcall))') converts to incompatible function type [-Wcast-function-type-mismatch]
```

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