My 8 year-old is like that, although not quite as severe. We are still working on it. I don't think anything can be done to suppress the initial inclination to cry, but he can control it somewhat based on social expectations. For example, he will usually stop almost immediately if asked. That sounds simple, but it doesn't occur to a lot of parents to ask.
Part of the problem in our case is inconsistency between the parents. My son rarely cries for me, because he knows it annoys me. However, my wife, knowing my son's tendency to cry easily, often assumes he is not really feeling bad about behavior she is correcting unless he is crying, so he cries very readily for her. My advice is to examine each parent's and caregiver's responses to see if you're encouraging it somehow.
The other thing to keep in mind is kids often cry because they don't know an alternative. You need to teach what to do, not just what not to do. I try to say something like:
I can't understand what you're saying if you cry. After you stop crying, then you can tell me what's wrong. Does crying help you get what you want? Does it make your sister stop teasing you? What do you think you could do instead?
This approach is gradually giving him fewer and fewer situations where he doesn't know what else to do but cry. Primarily it's when he gets in trouble now. Mostly, I'm just counting on him growing out of it as he gains emotional maturity. Seven or eight is still pretty young. I don't think there's cause for concern until after puberty.