Finally found the cause of make remaking unnecessary files after complete

Finally found the cause of make remaking unnecessary files after complete
building from scratch: when it compiles anything by combining several
pattern rules (which exactly what we use), it deletes some of the intermediate
files. The fix is to specify all of these files as ".SECONDARY", but beware,
these special targets don't understand patterns, so we have to list the
intermediates explicitly. Uff.