With "No package 'gtk+-2.0' found" error in making GGAP, you need to install gtk2's development package:
sudo apt-get install libgtk2.0-dev
With "XGAP needs XWindows X11R5 or better" error or other X11 header problems, the making of XGAP stops. Download and install xlibs-dev_7.2-0ubuntu11_all.deb
With "X11/Xaw/AsciiText.h: No such file or directory", etc. errors, do this: