BUG #15955: changes in pg_dump from 11.4 to 11.5

The following bug has been logged on the website:

Bug reference:      15955
Logged by:          sly
Email address:      cybersly7@hotmail.com
PostgreSQL version: 11.5
Operating system:   Linux
Description:

currently in the process of migrating a 8.1.23 to 11.x ( I know its
unsupported, long story)
these changes
(https://fossies.org/diffs/postgresql/11.4_vs_11.5/src/bin/pg_dump/pg_dump.c-diff.html)

now make it impossible to dump the old database from the new server.

ERROR:

pg_dump: reading dependency data
pg_dump: [archiver (db)] query failed: ERROR:  relation "pg_opfamily" does
not exist
pg_dump: [archiver (db)] query was: SELECT classid, objid, refclassid,
refobjid, deptype FROM pg_depend WHERE deptype != 'p' AND deptype != 'e'
UNION ALL
SELECT 'pg_opfamily'::regclass AS classid, amopfamily AS objid, refclassid,
refobjid, deptype FROM pg_depend d, pg_amop o WHERE deptype NOT IN ('p',
'e', 'i') AND classid = 'pg_amop'::regclass AND objid = o.oid AND NOT
(refclassid = 'pg_opfamily'::regclass AND amopfamily = refobjid)
UNION ALL
SELECT 'pg_opfamily'::regclass AS classid, amprocfamily AS objid,
refclassid, refobjid, deptype FROM pg_depend d, pg_amproc p WHERE deptype
NOT IN ('p', 'e', 'i') AND classid = 'pg_amproc'::regclass AND objid = p.oid
AND NOT (refclassid = 'pg_opfamily'::regclass AND amprocfamily = refobjid)
ORDER BY 1,2