[clang] [ASTContext] Add a break to nested switch in `encodeTypeForFunctionPointerAuth` (PR #99763)

[Brandon Wu via cfe-commits]

4vtomat wrote:

> Should we use unreachable If it's not possible to suppress the warning from gcc?
> 
> https://llvm.org/docs/CodingStandards.html#don-t-use-default-labels-in-fully-covered-switches-over-enumerations

Maybe, but I just want to keep the original semantic here since if the case was not presented, it's supposed to fall through rather than fail.

https://github.com/llvm/llvm-project/pull/99763