Hi Masahiro,

I love your patch! Yet something to improve:

[auto build test ERROR on kbuild/for-next]
[also build test ERROR on v5.6-rc7 next-20200326]
[cannot apply to sparc-next/master ipvs/master]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Masahiro-Yamada/kbuild-remove-AS-variable/20200326-034016
base:   https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git for-next
config: x86_64-randconfig-d002-20200326 (attached as .config)
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 4b428e8f18c7006f69b3d4ef0fdf091d998d0941)
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER=clang make.cross ARCH=x86_64 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> /bin/bash: --: invalid option
   Usage:	/bin/bash [GNU long option] [option] ...
   	/bin/bash [GNU long option] [option] script-file ...
   GNU long options:
   	--debug
   	--debugger
   	--dump-po-strings
   	--dump-strings
   	--help
   	--init-file
   	--login
   	--noediting
   	--noprofile
   	--norc
   	--posix
   	--pretty-print
   	--rcfile
   	--restricted
   	--verbose
   	--version
   Shell options:
   	-ilrsD or -c command or -O shopt_option		(invocation only)
   	-abefhkmnptuvxBCHP or -o option
   make[1]: *** [Makefile:1697: drivers] Error 2
   make[1]: Target '_all' not remade because of errors.
--
>> /bin/sh: 0: Illegal option --
   4 real  3 user  3 sys  164.71% cpu 	make distclean
--
>> /bin/sh: 0: Illegal option --
   3 real  0 user  1 sys  50.21% cpu 	make INSTALL_HDR_PATH=/tmp/usr/src/linux-headers-x86_64-randconfig-d002-20200326-e8c8c8d0ca995e05ef88ce20decd1c1134cda401 headers_install
--
>> /bin/sh: 0: Illegal option --
   14 real  3 user  9 sys  83.33% cpu 	make modules_prepare
--
>> /bin/sh: 0: Illegal option --
   4 real  3 user  1 sys  122.16% cpu 	make olddefconfig
--
>> /bin/sh: 0: Illegal option --
   21 real  21 user  11 sys  150.21% cpu 	make prepare

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org