Pull Kbuild updates from Masahiro Yamada:

 - Clean up Makefiles and scripts

 - Improve clang support

 - Remove unneeded genhdr-y syntax

 - Remove unneeded cc-option-align macro

 - Introduce __cc-option macro and use it to fix x86 boot code compiler
   flags

* tag 'kbuild-v4.13' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
  kbuild: improve comments on KBUILD_SRC
  x86/build: Specify stack alignment for clang
  x86/build: Use __cc-option for boot code compiler options
  kbuild: Add __cc-option macro
  kbuild: remove cc-option-align
  kbuild: replace genhdr-y with generated-y
  kbuild: clang: Disable 'address-of-packed-member' warning
  kbuild: remove duplicated arch/*/include/generated/uapi include path
  kbuild: speed up checksyscalls.sh
  kbuild: simplify silent build (-s) detection