reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux.git/commit/?id=a33bf4b6adf70aa8c8a18a231ea7aed3fd1b3875
        git remote add abelloni https://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux.git
        git fetch --no-tags abelloni rtc-next
        git checkout a33bf4b6adf70aa8c8a18a231ea7aed3fd1b3875

        # 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/rtc/