I soloed C'thun today and haven't seen any other warriors do it so i wanted to show that it can be done and explain how it can be done.
On the pull - Make sure to grab Ouro and bring him to C'thun's room and start the fight, this is for later in the fight.
Basically the phase 1, you nuke the eye, It isn't overly hard.
Phase 2 however, you dps C'thun and he will take 99% reduced damage. Eventually he will eat you, but Ouro will pull you out of C'thun's stomach because he can't attack you. However, the stacking debuff will build up because the game thinks you are still inside, that is the hard part.(Note if you don't have Ouro you die after 7 secs)
You'll need impending victory and Blood craze to survive the damage. When you are about 35% pop enraged regen and last stand and continue to dps, the next time you get to like 60% with those 2 abilities on CD you should run around and use only devastate on the eye tentales - For whatever reason they proc Impending victory ( heals for about 25k with the glyph in my gear) even though the devastate one shots them.
Eventually the boss will eat you again, Ouro will teleport you out and it repeats ( There can be a very random gap between 1 digest to another, it can be really short ( 5mins or so) or very long ( 20minutes or so)) so with that in mind, be ready to use your cooldowns early, so that they will be up again when you infact need them. Run around and devastate for heals, once the boss goes under 20% just stay on him full time and dps him down, healing with victory rush.
This fight takes an incrediably long time to complete ( 1hour 58minutes in my case), so be prepared!
The video is sped up otherwise its a very very very long fight to watch. lol.
Also, ensure you bring a second main hand and 1-2 extra shields!
(I did not come up with the idea of how to stay out of the stomach, the original strat came from Jider the rogue who soloed it)