Titan Bloodline at level 12, can handle Huge weapons.
That ability applies only to Warhammers.
If your DM is that much of a dick than you have far greater problems. There's as much to suggest it's warhammers-only as otherwise, since the entry is always for the specific creature.
There's as much to suggest that it only works for one size category above you.
Which is completely fine with me.
The SRD Titan has Oversized Weapon, keyed to the Warhammer.
And it later says "The titan retains its oversized weapon special attack regardless of form."
The Elder Titan has the same abilities, but it doesn't mention a specific weapon.
It's stat block has listed the Warhammer though.
The Cloud Giant has Oversized Weapon, keyed to the MorningStar.
Same with the Skeleton of a Cloud Giant.
And it's a Special Ability for the Titans, and a Special Quality for the Cloud Giants.
For the Titian Bloodline, it doesn't have a specific weapon listed, footnoting a direct mention of the Titan's ability.
What I take from this is the ability is: Oversized Weapon, and then you pick the one weapon.
is a possible understanding.
I see how it could be understood as JaronK said: Oversized Weapon no picking which weapon.
And clearly the editing of the entries is as waffle-ly as any other.
I'm not sure what to make of Prime 32's idea.
The Titan can shapechange into a smaller size, but doesn't lose the Gargantuan weapon.
Verges on rules I haven't read up on lately.
