If gtk3 and all of its deps are installed correctly, you should see something like this: $ pkg-config --cflags gtk+-3.0
-pthread -I/usr/local/include/gtk-3.0 -I/usr/local/include/at-spi2-atk/2.0 -I/usr/local/include/at-spi-2.0 -I/usr/local/include/dbus-1.0 -I/usr/local/lib/dbus-1.0/include -I/usr/local/include/gtk-3.0 -I/usr/local/include/gio-unix-2.0/ -I/usr/local/include -I/usr/local/include/cairo -I/usr/local/include -I/usr/local/include/pango-1.0 -I/usr/local/include/fribidi -I/usr/local/include/atk-1.0 -I/usr/local/include/cairo -I/usr/local/include/pixman-1 -I/usr/local/include -I/usr/local/include/freetype2 -I/usr/local/include/harfbuzz -I/usr/local/include -I/usr/local/include/libdrm -I/usr/local/include -I/usr/local/include/libpng16 -I/usr/local/include -I/usr/local/include/gdk-pixbuf-2.0 -I/usr/local/include/libpng16 -I/usr/local/include/glib-2.0 -I/usr/local/lib/glib-2.0/include -I/usr/local/include -I/usr/include/uuid -I/usr/local/include
what do you get?
Note that this should be enough to achieve the above: $ tce-load -i compiletc gtk3-dev