Because bmake defaults to .../share/mk now, this code was not doing anything
to help objdir builds (such as the rescue build). Export the same default.
Sponsored by: EMC / Isilon Storage Division
See r298220 for more explanation. We don't want to prevent installing
if a cookie exists for the install target.
Sponsored by: EMC / Isilon Storage Division
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
