The error occurs at lines 1429 & 1476. Libbfd is described at Wikipedia
and there are plenty of hits from google.
It's got to be the "slackware" component of the name, right? It's set at line 130 (i.e. log line 130) for build and host systems and then the target system is set. Perhaps you need to edit the Makefile and insert a sed clause that removes the "-slackware" component so that the BFD clause changes from i486-slackware-linux-gnu to i486-linux-gnu, assuming it is set with a make or shell command.
Could be the blind leading the blind here, but that would be my first attempt to fix it. Also, I happened to note while going through some man pages the following
archive_entry_uname  (3) - functions for manipulating archive entry descriptions
archive_entry_uname  (3p) - functions for manipulating archive entry descriptions
libarchive  (3) - functions for reading and writing streaming archives
libarchive  (3p) - functions for reading and writing streaming archives
libarchive  (5) - formats - archive formats supported by the libarchive library
libarchive_internals  (3) - description of libarchive internal interfaces
libarchive_internals  (3p) - description of libarchive internal interfaces
which may be relevant since your errors are coming from ar.