Merge git://git.kernel.org/pub/scm/linux/kernel/git/sam/kbuild-next
* git://git.kernel.org/pub/scm/linux/kernel/git/sam/kbuild-next:
kbuild: ignore a few files in headers_check
kbuild: add checks for include of linux/types in userspace headers
kbuild: drop debugging leftover in tags.sh
kbuild: document environment variables
kbuild: make *config usage docs
kbuild: disable sparse warning "returning void-valued expression"
kbuild: in headers_install autoconvert asm/inline/volatile to __xxx__
kbuild: check for leaked CONFIG_ symbols to userspace
headers_check.pl: disallow extern's
kconfig: improve error messages for bad source statements
kconfig: struct property commented
kconfig: add comments to symbol flags
kconfig: explain symbol value defaults
m68k: fix recursive dependency in Kconfig