You need to setup the gcw0 buildroot first: Download a precompiled toolchain from http://www.gcw-zero.com/develop.
You need to cross-compile pixman.
Download Player and liblcf from GitHub:
git clone --depth=1 https://github.com/EasyRPG/Player.git
cd Player/libs
git clone --depth=1 https://github.com/EasyRPG/liblcf.git
cd ..
Change into the builds/opendingux
folder and start the build:
cd builds/opendingux
make
If no error occured, there will be an EasyRPG executable in the gcw-zero
subdirectory. To build an opk ready to deploy to the device:
cd gcw-zero
./opk_build.sh