reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/jirislaby/linux.git/commit/?id=7c9b7cd343b314fdb523ff791b9852f0b2b05b6a
        git remote add jirislaby https://git.kernel.org/pub/scm/linux/kernel/git/jirislaby/linux.git
        git fetch --no-tags jirislaby devel
        git checkout 7c9b7cd343b314fdb523ff791b9852f0b2b05b6a
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash drivers/tty/serial/8250/