flash_FP4_factory.sh: Support MacOS

      FASTBOOT_BIN="${ROOT_DIR}/bin-linux-x86/fastboot"

      ;;

    msys|MINGW*)

      echo "INFO: You are using MinGW on Windows"

      echo "INFO: You are using MinGW on Windows."

      FASTBOOT_BIN="${ROOT_DIR}/bin-msys/fastboot.exe"

      ;;

    Darwin)

      echo "INFO: You are using MacOS."

      FASTBOOT_BIN="${ROOT_DIR}/bin-darwin/fastboot"

      ;;

    *)

      echo "ERROR: Unsupported operating system (${OSTYPE})."

      echo "ERROR: Only GNU/Linux, and MinGW on Windows are currently supported."

      echo "ERROR: Only GNU/Linux, MacOS, and MinGW on Windows are currently supported."

      abort_now

      ;;

  esac