I've always pronounced it as "GulBigOhLib"
I mean, that's how it seems to be spelled.
...I could be completely wrong though.
While I have never pronounced it ever, here's how I would after thinking it over;
Gl'b (apostrophe marks an unnatural shortening at the end and start of the letters either side- gllob (Imagine the spanish pronunciation of the sound ll makes)
so like some other person said for the first part, g?lb' gol(oi)b
for the second part start with goilb
and then make the oi really quiet and switch where the l is
....sorta... well it seems like it to me, and you have to admit it makes sense and yeah i'm arguing a hopeless case here. still, i find glubogolyb easier to pronounce than Gl'bgolyb.
I pronounce it Glb(with no vowel)-go-lib.