When I tried the emerging GIMP 2.3.9, it told me to install app-text/poppler with the gtk USE flag: * This package requires app-text/poppler compiled with GTK+ support. * Please reemerge app-text/poppler with USE="gtk". But app-text/poppler does not contain a "gtk" USE flag. SOLUTION: It is was meant to compile app-text/poppler-bindings with the "gtk" USE flag, therefore simply change the upper advice text in the ebuild and everything will be fine.
I fixed this in gimp-9999.ebuild, but forgot to backport it to 2.3.9. Thank you for reporting this! :) Fixed in CVS.