Pull kbuild updates from Michal Marek:

 - new option CONFIG_TRIM_UNUSED_KSYMS which does a two-pass build and
   unexports symbols which are not used in the current config [Nicolas
   Pitre]

 - several kbuild rule cleanups [Masahiro Yamada]

 - warning option adjustments for gcov etc [Arnd Bergmann]

 - a few more small fixes

* 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild: (31 commits)
  kbuild: move -Wunused-const-variable to W=1 warning level
  kbuild: fix if_change and friends to consider argument order
  kbuild: fix adjust_autoksyms.sh for modules that need only one symbol
  kbuild: fix ksym_dep_filter when multiple EXPORT_SYMBOL() on the same line
  gcov: disable -Wmaybe-uninitialized warning
  gcov: disable tree-loop-im to reduce stack usage
  gcov: disable for COMPILE_TEST
  Kbuild: disable 'maybe-uninitialized' warning for CONFIG_PROFILE_ALL_BRANCHES
  Kbuild: change CC_OPTIMIZE_FOR_SIZE definition
  kbuild: forbid kernel directory to contain spaces and colons
  kbuild: adjust ksym_dep_filter for some cmd_* renames
  kbuild: Fix dependencies for final vmlinux link
  kbuild: better abstract vmlinux sequential prerequisites
  kbuild: fix call to adjust_autoksyms.sh when output directory specified
  kbuild: Get rid of KBUILD_STR
  kbuild: rename cmd_as_s_S to cmd_cpp_s_S
  kbuild: rename cmd_cc_i_c to cmd_cpp_i_c
  kbuild: drop redundant "PHONY += FORCE"
  kbuild: delete unnecessary "@:"
  kbuild: mark help target as PHONY
  ...