The problem is most likely pkgconfig. Autoconf uses pkgconfig to locate installed libraries, which it does by consulting .pc files stored in a specific directory. Installing a new library installs the .pc file for it, and everything works great.
Works great, that is, except when pkgconfig is looking at a custom readonly directory - e.g. part of a mounted disk image. Oops.
Try copying everything from /opt/native/arm/3.4.5-xscale-softvfp/armv5tel-cacko-linux/lib/pkgconfig to /usr/lib/pkgconfig (don't overwrite any .pc files already there!) and then set the PKG_CONFIG environment variable to point to /usr/lib/pkgconfig. Like this:
PKG_CONFIG=/usr/lib/pkgconfig ./configure <configure opts>
If you've compiled your libraries with autoconf and done a "make install" then IIRC the .pc file will be installed to /usr/lib/pkgconfig. But it might make sense to check /usr/local/lib/pkgconfig and move anything you find there just in case
This didn't completely help me - for some reason gcc *insisted* on using the headers in the image instead of the local ones, even when I explicitly set all the include paths. Hopefully you won't hit that problem; I needed to do Stupid Mount Tricks to fix it...