Seems like the gtk and gtk2 use flags are a little excessive in xscreensaver-4.14-r1.ebuild.
Created attachment 25838 [details, diff] patch to tidy the gtk and gtk2 use flags. I believe this results in a cleaner, yet equivalent USE flag checking.
this patch still applies to xscreensaver-4.14-r2.ebuild
yep, rest assure, i know i've got to handle this issue. but -r2 was a security update and i don't want to introduce anything new except for the necessary patches since this is going straight to stable.
in xscreensaver-4.15. thanks for the patch