META_MODE: Default OBJROOT to the traditional /usr/src/SRCTOP/.

META_MODE: Default OBJROOT to the traditional /usr/src/SRCTOP/.

This avoids easily colliding multiple src trees with the same objects.  Having
multiple checkouts in dir/ dir2/ dir3/ would all use obj/ without any unique
identifier inside of obj/.  This pattern is more likely to be used due
to the non-META_MODE behavior working with it fine.

In environments where ../obj/ is wanted as the obj directory the value of
OBJROOT can be set to ${SRCTOP:H}/obj/ instead via src-env.conf (set by
SRC_ENV_CONF) or environment.  For environment it must be single quoted or
escaped.  This will be more likely for vendors who are building images or using
NFS for builds.  In those cases MAKEOBJDIRPREFIX may already be utilized and
is supported.

Discussed with:	imp
Sponsored by:	EMC / Isilon Storage Division