I support abortion on the basis of the fundamental libertarian principle of self-ownership: I own my body; hence I am free to dispose of it as I will. There is no legitimate grounding in libertarian philosophy for opposing the right to choose. Can someone 'compromise' on it? Certainly. And that person is not a libertarian.
I love it when the average internet joe tries to zealously define libertarianism in his eyes and claim that everyone else is wrong and not a libertarian.
Try this: one of the most agreed upon principles of libertarianism is that you do not bring about pre-emptive violence. So, by killing a person when he/she is still inside of the mother's womb, you are commiting an aggresive act of interventionist violence to terminate a life. That personally doesn't sound like a very libertarian idea to me, but I'll digress.