iPhone On-Device Toolchain

copy contents of /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.0.sdk from official SDK to /var/sdk on iPhone
Install apt from Cydia
pushd /var/sdk/usr/lib
ln -s libgcc_s.1.dylib libgcc_s.10.5.dylib
ln -s dylib1.o dylib1.10.5.o
ln -s crt1.o crt1.10.5.o
ln -s libstdc++.6.0.9.dylib libstdc++.6.dylib
ln -s libstdc++.6.0.9.dylib libstdc++.dylib
ln -s libobjc.A.dylib libobjc.dylib
ln -s libSystem.B.dylib libSystem.dylib
popd
apt-get install curl git make ldid less com.ericasadun.utilities adv-cmds top rsync
curl http://apt.saurik.com/cydia/debs/libgcc_4.2-20080410-1-6_iphoneos-arm.deb -o libgcc.deb
dpkg -i libgcc.deb
rm libgcc.deb
apt-get install iphone-gcc