[clang] [libclc] [Clang] Rename elementwise builtins to `clzg` and `ctzg` (PR #157128)

[Nikolas Klauser via cfe-commits]

https://github.com/philnik777 commented:

FWIW I'm in favour of the renaming. Having consistent naming for the `__builtin_elementwise_*` and `__builtin_*` functions is IMO much more valuable than being consistent with compiler-internal naming.

https://github.com/llvm/llvm-project/pull/157128