MFC r250143, r257079, r258086, r262670:
r250143 (benno):
Optimize SUBDIR_OVERRIDE such that SUBDIR isn't automatically
defined if SUBDIR_OVERRIDE is defined.
r257079:
Fix build host pollution by avoiding calling 'uname -srp' to
determine values for 'VERSION'.
r262670 (marcel):
Use ${MAKE} so that we always use the same version/implementation
of make.
r258086 (cperciva):
Strip the -pN patch level from the VERSION string which gets
encoded into CTF data. Otherwise FreeBSD Update builds think every
kernel file has changed every time there's a security advisory,
since the FreeBSD Update build code isn't smart enough to look inside
CTF data to ignore those changes.
Tested on: stable/9@r263881
Sponsored by: The FreeBSD Foundation
git-svn-id: svn://svn.freebsd.org/base/stable/9@264014
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