The following assumes that you have a working cross-build environment for avr-gcc.
# Change current directory to the root of the Papageno git repository
#
cd <papageno_git_root>
# Create and switch to a build directory (always prefer out-of-source builds)
#
mkdir -p build/avr-gcc
cd build/avr-gcc
# Configure for cross-plaform
#
cmake -DCMAKE_TOOLCHAIN_FILE=$PWD/../../cmake/toolchains/Toolchain-avr-gcc.cmake ../..
# Run the build
#
make
This will create a library libpapageno.a in <papageno_git_root>/build/avr-gcc/src.