This changes the build OBJDIR from the older style of /usr/obj/<srcdir> for
native builds, and /usr/obj/<target>.<target_arch>/<srcdir> for cross builds to
a new simpler format of /usr/obj/<srcdir>/<target>.<target_arch>. This
new format is used regardless of cross or native build.
The UNIFIED_OBJDIR option will be removed and its feature made permanent
for the 12.0 release.
Relnotes: yes (don't note UNIFIED_OBJDIR option since it will be removed)
Prior work: D3711 D874
Sponsored by: Dell EMC Isilon
The UNIFIED_OBJDIR option is intended to be a temporary migration option.
Uses and expands some of the DIRDEPS_BUILD logic, moved in rS325191.
AUTO_OBJ is _not enabled_ in this commit, D12841 handles it.