Create something that might be usable as a symbol list for bochs'
internal debugger.

getting suppressed.  :(

Change from using #if to #ifdef, since #if can't cope with string
constants.

Don't use -MP to generate phony rules for included files, otherwise
make won't use the pattern rule for config/%.h.  :(

header files.

trick with "touch -B 2" doesn't work because the file that we're
carefully timestamping just gets deleted anyway.

list for any build, e.g.
  make bin/pnic.dsk DEBUG=pci,pnic
This will drag in debugging-enabled versions of pci.c and pnic.c.

Add bin/%.rebuild rule to quickly force a rebuild of any file.

Add bin/%.o.dbg rule to build a debugging-enabled version of the object.

conflict with pci_device function.