gtk3 @3.24.41_2+quartz: review active_variants check against glib2

[cooljeanius (Eric Gallager)]

Basically, see discussion on commit ​d0aca00. I can understand doing the variant check one way around for the missing symbol, but that doesn't necessarily mean it's necessary to do it the other way around, too. I have gtk3 installed with +quartz and glib2 installed with +x11 and this is breaking upgrading of all of my gnome ports. Getting issue #63680 fixed would probably resolve this.