Follow-up r325329: Store all WORLDTMP objects back in the same directory.

This still keeps the reduced MAKEOBJDIRPREFIX (SRCTOP) redundancy
removed in the OBJDIR, but now keeps all early phase objects
in the same directory rather than split per phase.

The problem of splitting per phase is that later phases want to link in
libraries from earlier phases and base their location on ${OBJTOP}.

Pointyhat to: bdrewery
Reported by: mjoras, Mark Millard
Sponsored by: Dell EMC Isilon