You might not have it installed, or you might now have the -devel version necessary (the headers) that it looks for. You can [usually] point it to the location of the missing file(s) with something like:
./configure --enable-gui --enable-gtk=/usr/local/whatever
OR, you might just have gtk2, check the configure options to see if you need to specify which gtk to use:
./configure --help
Cool
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