[PATCH v2] kbuild: move -Wundef from KBUILD_CFLAGS to KBUILD_CPPFLAGS

[kernel test robot]

Hi Masahiro,

I love your patch! Perhaps something to improve:

[auto build test WARNING on masahiroy-kbuild/for-next]
[also build test WARNING on s390/features soc/for-next linus/master v6.0-rc6]
[cannot apply to next-20220921]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Masahiro-Yamada/kbuild-move-Wundef-from-KBUILD_CFLAGS-to-KBUILD_CPPFLAGS/20220913-161447
base:   https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git for-next
config: arm64-buildonly-randconfig-r003-20220922 (https://download.01.org/0day-ci/archive/20220923/202209231052.nj1STd5X-lkp@intel.com/config)
compiler: aarch64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/ccf1a82d3dedb27a2b1b21f64e09183b197e1f6f
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Masahiro-Yamada/kbuild-move-Wundef-from-KBUILD_CFLAGS-to-KBUILD_CPPFLAGS/20220913-161447
        git checkout ccf1a82d3dedb27a2b1b21f64e09183b197e1f6f
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm64 SHELL=/bin/bash arch/arm64/kernel/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp at intel.com>

All warnings (new ones prefixed by >>):

   In file included from arch/arm64/kernel/vmlinux.lds.S:65:
>> arch/arm64/include/asm/kernel-pgtable.h:135:41: warning: "PMD_SHIFT" is not defined, evaluates to 0 [-Wundef]
     135 | #define ARM64_MEMSTART_SHIFT            PMD_SHIFT
         |                                         ^~~~~~~~~
   arch/arm64/include/asm/kernel-pgtable.h:144:5: note: in expansion of macro 'ARM64_MEMSTART_SHIFT'
     144 | #if ARM64_MEMSTART_SHIFT < SECTION_SIZE_BITS
         |     ^~~~~~~~~~~~~~~~~~~~


vim +/PMD_SHIFT +135 arch/arm64/include/asm/kernel-pgtable.h

87d1587bef394c Suzuki K. Poulose 2015-10-19  122  
a7f8de168ace48 Ard Biesheuvel    2016-02-16  123  /*
a7f8de168ace48 Ard Biesheuvel    2016-02-16  124   * To make optimal use of block mappings when laying out the linear
a7f8de168ace48 Ard Biesheuvel    2016-02-16  125   * mapping, round down the base of physical memory to a size that can
a7f8de168ace48 Ard Biesheuvel    2016-02-16  126   * be mapped efficiently, i.e., either PUD_SIZE (4k granule) or PMD_SIZE
a7f8de168ace48 Ard Biesheuvel    2016-02-16  127   * (64k granule), or a multiple that can be mapped using contiguous bits
a7f8de168ace48 Ard Biesheuvel    2016-02-16  128   * in the page tables: 32 * PMD_SIZE (16k granule)
a7f8de168ace48 Ard Biesheuvel    2016-02-16  129   */
06e9bf2fd9b372 Ard Biesheuvel    2016-03-30  130  #if defined(CONFIG_ARM64_4K_PAGES)
06e9bf2fd9b372 Ard Biesheuvel    2016-03-30  131  #define ARM64_MEMSTART_SHIFT		PUD_SHIFT
06e9bf2fd9b372 Ard Biesheuvel    2016-03-30  132  #elif defined(CONFIG_ARM64_16K_PAGES)
ca6ece6a76a8b5 Anshuman Khandual 2021-06-14  133  #define ARM64_MEMSTART_SHIFT		CONT_PMD_SHIFT
a7f8de168ace48 Ard Biesheuvel    2016-02-16  134  #else
06e9bf2fd9b372 Ard Biesheuvel    2016-03-30 @135  #define ARM64_MEMSTART_SHIFT		PMD_SHIFT
06e9bf2fd9b372 Ard Biesheuvel    2016-03-30  136  #endif
06e9bf2fd9b372 Ard Biesheuvel    2016-03-30  137  

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