reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://git.kernel.org/pub/scm/linux/kernel/git/cip/linux-cip.git/commit/?id=6a3ed2167f29d8e8e97da9b95787fa25261ae1e4
        git remote add cip https://git.kernel.org/pub/scm/linux/kernel/git/cip/linux-cip.git
        git fetch --no-tags cip b-4.4-st56-rt51
        git checkout 6a3ed2167f29d8e8e97da9b95787fa25261ae1e4
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-7.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=parisc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-7.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=parisc SHELL=/bin/bash drivers/char/ kernel/ lib/