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

[Joseph Huber via cfe-commits]

jhuber6 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.

Should be done, I just kept the same name inside the source though.

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