glu.h -- Silence warnings

[MrBcx]

A minor update that silences strict warnings - 3 instances replacing () with (void).

[Robert]

A minor update that silences strict warnings - 3 instances replacing () with (void).

Silencing nothing with a void.
An interesting concept to contemplate.
It fits well into the Zen class of "koan".

Thanks for this, warnings make me nervous.