It's weird that the compiler on slitaz online cooker cannot see the gtk+ and the required libs or source files. However the required libs and source files exists on the slitaz cooker.
See the following sample package details from the cooker.
http://cook.slitaz.org/cooker.cgi?pkg=audacious-plugins
http://cook.slitaz.org/cooker.cgi?pkg=Xdialog
http://cook.slitaz.org/cooker.cgi?pkg=aqualung
http://cook.slitaz.org/cooker.cgi?pkg=avant-window-navigator
