reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/commit/?id=52d2af10759262ab95162ddc1a56faa8fe3aabde
        git remote add bluetooth-next https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git
        git fetch --no-tags bluetooth-next master
        git checkout 52d2af10759262ab95162ddc1a56faa8fe3aabde
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/bluetooth/