[clang] [llvm] [PowerPC] Add builtin_cpu_is P11 support (PR #99550)

[David Tenty via cfe-commits]

daltenty wrote:

> > Should there be a lit test for the linux part as well?
> 
> Is there a pre-existing test already, or should I add a new one? I can't seem to find an equivalent to `clang/test/CodeGen/aix-builtin-cpu-is.c`

There's an existing `ppc64le` block in `clang/test/CodeGen/builtin-cpu-supports.c`, I think we should just add the missing cases for Power8+ there.

https://github.com/llvm/llvm-project/pull/99550