Okay, I'll answer all of your questions in order.
First, the ability Flame Body halves the steps you have to take to hatch an egg and has nothing to do with shininess. If you want shinies, get the shiny charm and try chaining or Masuda.
Second, Garchomp and Pansear cannot breed together since they're in different egg groups. (Good point, EnergyZebra)
And finally, the species of a breeded Pokémon is always that of the female parent, so if your Garchomp is female, you can breed it with anything in its egg group to give you a Gible. If it's male, you'll have to breed with Ditto.