[clang] [clang] move -Wcast-function-type under -Wextra (PR #77178)

[Amy Kwan via cfe-commits]

amy-kwan wrote:

I believe this patch is causing some issues on two PPC bots. Would you be able to help take a look?
https://lab.llvm.org/buildbot/#/builders/57/builds/33601/steps/5/logs/stdio
https://lab.llvm.org/buildbot/#/builders/36/builds/43759/steps/12/logs/stdio

https://github.com/llvm/llvm-project/pull/77178