Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Move include of make.conf back to its old position.

This means moving include of local.sys.mk and src.sys.mk too.
Introduce new includes to take the early slot, for the purpose
of being able to influence toolchains and the like.

Differential Revision: D2860
Reviewed by: imp

Skip MAKE_PRINT_VAR_ON_ERROR unless we are doing META_MODE
with all the recursion in normal build it is too much noise.

Add META_MODE support.

Off by default, build behaves normally.
WITH_META_MODE we get auto objdir creation, the ability to
start build from anywhere in the tree.

Still need to add real targets under targets/ to build packages.

Differential Revision: D2796
Reviewed by: brooks imp