Make sure that there is an environment variable called DEVKITARM with the path of the directory before the "bin" directory containing "arm-none-eabi-as", "arm-none-eabi-cpp", "arm-none-eabi-ld" and "arm-none-eabi-objcopy".
Then get the compiler from https://github.com/pret/agbcc and run the following commands.
Then get the compiled tools from https://github.com/pret/pokeruby-tools. Copy the `tools/` folder over the `tools/` folder in your pokeemerald directory.