In one setting I'm using, Warlock refers to a mage that fights on the front lines in battle.

As for what I would call a male witch. Well in the context of D&D I'd probably just call them all witches, just like you call female wizards by the same name. Otherwise I'd generally just use Warlock. Witch hardly means anything positive in etymology any more than warlock does. I also fail to see how the existence of a male term is in of itself somehow sexist. Especially considering witch is still the norm. It's not like anyone's trying to commandeer the word and start calling female witches warlockesses or something dumb like that.