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* lib/Makefile.in (clean): Remove *-t files.
(mostlyclean): Remove MOSTLYCLEANFILES that are not *-t files.
This removes files like lib/getopt.h that should be removed
even if this configuration did not need to build them.
(maintainer-clean): Remove TAGS here, not in distclean,
to be consistent with ../src/Makefile.in.