This file is included several times in a row, once
for each element of $(object-suffixes). $(object-suffixes-left)
is initialized first to $(object-suffixes) so that with each
inclusion, we advance $o to the next suffix.
o := $(firstword $(object-suffixes-left))
object-suffixes-left := $(filter-out $o,$(object-suffixes-left))
$(o-iterator-doit)