I think there's a difference between "hiring only men/women" and "advertising to only men/women". A company could launch a recruitment campaign which is only visible to one gender, but still not discriminate against applicants from the opposite gender. Presumably they have many more ways to list job openings than targeted Facebook ads, so they're not specifically excluding one gender from that job; just from the ad.

What if you spend the same amount of money but create separate ads targeted at men and women?

What if you are trying to get more female engineers at your company, and want to target women?

Isn’t it discriminatory to have an intent to discriminate based on gender? “We want more <gender> at our company.” Unless gender is a bonafide qualification, that should be illegal just as “we want to hire more white people.”

Right, but let's go with the premise that you have an imbalance, and are trying to bring into balance. Then a gender or race targeted ad seems like a reasonable approach.

I guess my point is an targeted ad isn't evidence of intent to discriminate, and in fact can be a key component of pro-diversity actions.