My initial reaction is to ask how I could have run make if I didn't install the devel packages... But honestly, I know so little that I suppose it's possible that I could run make, but still not have "all" the devel packages installed.
Well, yeah. You need compilers, but you also need the GTK devel packages, and probably even the X devel packages, etc etc etc. Generally I just install all the devel packages when I do the install.
All I know is that compiling programs isn't as hard as it's made out to be (unless it's some strange program that doesn't use automake, but those are fairly rare), so there must be something seriously wrong with your system. :)
Then again, I'm coming from a Linux From Scratch background, which is like gentoo except you do everything by hand and there is no fancy installer to hold your hand in the process :)
