Pull Kbuild updates from Masahiro Yamada:

 - Use Make-builtin $(abspath ...) helper to get absolute path

 - Add W=2 extra warning option to detect unused macros

 - Use more KCONFIG_CONFIG instead hard-coded .config

 - Fix bugs of tar*-pkg targets

* tag 'kbuild-v4.14' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
  kbuild: buildtar: do not print successful message if tar returns error
  kbuild: buildtar: fix tar error when CONFIG_MODULES is disabled
  kbuild: Use KCONFIG_CONFIG in buildtar
  Kbuild: enable -Wunused-macros warning for "make W=2"
  kbuild: use $(abspath ...) instead of $(shell cd ... && /bin/pwd)