[clang] [Clang][NFC] Introduce `gpulib` positive flag for `nogpulib` (PR #126567)

[Artem Belevich via cfe-commits]

Artem-B wrote:

If we're adding new options, I'd prefer those to be the standard double-dash options, rather than adding a special case to the legacy-style option.

Also, we still have the original `-nocudalib` being aliased to `-nogpulib`. We should probably take care of that, too. 



https://github.com/llvm/llvm-project/pull/126567