You can build the existing harnesses either for libfuzzer or AFL++.
Building the fuzzers requires clang (libfuzzer) or an installed version
of AFL++.
mkdir build_libfuzzer && cd build_libfuzzer
cmake -DENABLE_FUZZING=ON ..export CC=afl-clang-fast
export CXX=afl-clang-fast++
mkdir build_afl && cd build_afl
cmake -DENABLE_FUZZING=ON -DUSE_AFLPLUSPLUS=ON ..