signalbackup-tools: use new `--config` option in build script

  buildInputs = [ openssl sqlite ];

  # Manually define `CXXFLAGS` and `LDFLAGS` on Darwin since the build scripts includes flags

  # that don't work on Darwin.

  buildPhase = ''

    runHook preBuild

  '' + lib.optionalString stdenv.isDarwin ''

    export CXXFLAGS="-Wall -Wextra -Wshadow -Wold-style-cast -Woverloaded-virtual -pedantic -O3"

    export LDFLAGS="-Wall -Wextra -O3"

  '' + ''

    ./BUILDSCRIPT_MULTIPROC.bash44

    ./BUILDSCRIPT_MULTIPROC.bash44${lib.optionalString stdenv.isDarwin " --config nixpkgs-darwin"}

    runHook postBuild

  '';