rebar.config

{port_specs, [
    {"priv/b64url.so", ["c_src/*.c"]}
]}.

{eunit_opts, [verbose]}.

{port_env, [
    % Development compilation
    % {".*", "CFLAGS", "$CFLAGS -g -Wall -Werror -fPIC"}

    % Production compilation
    {".*", "CFLAGS", "$CFLAGS -Wall -Werror -DNDEBUG -O3"}
]}.