Ok. The problem is that the config program that is compiled and linked to test the GTK version is failing to link.
The problem is the lack of libXext, as this config.log snippet shows:
configure:1636: gcc -o conftest -g -O2 -I/opt/arm/3.3.2/armv5tel-cacko-linux/include/gtk-1.2 -I/opt/arm/3.3.2/armv5tel-cacko-linux/include/glib-1.2 -I/opt/arm/3.3.2/armv5tel-cacko-linux/lib/glib/include -I/opt/arm/3.3.2/armv5tel-cacko-linux/X11R6/include -Wl,-rpath-link,/opt/arm/3.3.2/armv5tel-cacko-linux/X11R6/lib conftest.c -L/opt/arm/3.3.2/armv5tel-cacko-linux/lib -L/opt/arm/3.3.2/armv5tel-cacko-linux/X11R6/lib -lgtk -lgdk -rdynamic -lgmodule -lglib -ldl -lXext -lX11 -lm -Wl,-rpath-link,/opt/arm/3.3.2/armv5tel-cacko-linux/X11R6/lib 1>&5
/usr/bin/ld: skipping incompatible /opt/arm/3.3.2/armv5tel-cacko-linux/lib/libgtk.so when searching for -lgtk
/usr/bin/ld: skipping incompatible /opt/arm/3.3.2/armv5tel-cacko-linux/lib/libgdk.so when searching for -lgdk
/usr/bin/ld: skipping incompatible /opt/arm/3.3.2/armv5tel-cacko-linux/lib/libgmodule.so when searching for -lgmodule
/usr/bin/ld: skipping incompatible /opt/arm/3.3.2/armv5tel-cacko-linux/lib/libglib.so when searching for -lglib
/usr/bin/ld: skipping incompatible /opt/arm/3.3.2/armv5tel-cacko-linux/lib/libdl.so when searching for -ldl
/usr/bin/ld: skipping incompatible /opt/arm/3.3.2/armv5tel-cacko-linux/lib/libdl.a when searching for-ldl
/usr/bin/ld: skipping incompatible /opt/arm/3.3.2/armv5tel-cacko-linux/X11R6/lib/libXext.so when searching for -lXext
/usr/bin/ld: cannot find -lXext
And yet, the library is there:
sh-2.05b$ find /opt/arm/3.3.2/armv5tel-cacko-linux/ -name libXext* -print
/opt/arm/3.3.2/armv5tel-cacko-linux/X11R6/lib/libXext.so
So, I am confused now...