Allow caller to pass a TARGET_SPEC which may be more complex than
just MACHINE, for recognizing objects which do not need qualifying
in dirdeps.
Keep dirdeps for pseudo machines like "host" and "common" simple.
Also we need to use DEP_MACHINE_ARCH when expanding CSU_DIR
If TARGET_OBJ_SPEC is no just MACHINE, pass it to meta2deps.py
Cleanup some backwards compat stuff we do not need.
Introduce TARGET_OBJ_SPEC (derrived from TARGET_SPEC_VARS)
so we can build something like universe.