If for any reason we cannot set .OBJDIR==_objdir as desired
use .CURDIR so that at least the classic
.if ${.OBJDIR} != ${.CURDIR}
works and dangerous misstakes can be avoided.
Reviewed by: bdrewery
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
