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

[Amy Kwan via cfe-commits]

amy-kwan wrote:

Hi @Abhinkop!
I was wondering if there was any progress regarding the patch to resolve the stage 2 failure, as our bot is still red (https://lab.llvm.org/buildbot/#/builders/36/builds/43929/steps/12/logs/stdio).
Please let me know if you would also like me to test any patches, as well. 

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