With CONFIG_MODVERSIONING, we need to record the versions of the unresolved
symbols in the final <module>.ko, which we only know after we finished
the descending build. So we only build <module>.o in that case.
  
Also, keep track of the modules we built, the post-processing step needs
a list of all modules. Keeping track is done by touching
.tmp_versions/path/to/module.ko