Just compile fontconfig and install it inside the toolchain:
./configure --prefix=/usr --host=mipsel-linux
make install DESTDIR=/opt/gcw0-toolchain/usr/mipsel-gcw0-linux-uclibc/sysroot
Then you will be able to compile programs that use it.
I don't recommend to compile statically, it's generally not a good idea. Instead, you can put the .so of the libraries you just compiled in the OPK if they are not already in the rootfs, and set the library search path accordingly on the Exec line of your .desktop:
Exec=env LD_LIBRARY_PATH=. ./myapp