pg_dump/pg_restore seem broken on hamerkop

Buildfarm member hamerkop has been failing in the pg_upgrade regression
test for the last several days. The problem looks like this:

command: "C:/buildfarm/build_root/HEAD/pgsql.build/contrib/pg_upgrade/tmp_check/install/bin/pg_restore" --port 50432 --username "Administrator" --exit-on-error --verbose --dbname "postgres" "pg_upgrade_dump_12145.custom" >> "pg_upgrade_dump_12145.log" 2>&1
pg_restore: connecting to database for restore
pg_restore: [archiver (db)] Error while INITIALIZING:
pg_restore: [archiver (db)] could not execute query: ERROR: invalid byte sequence for encoding "UTF8": 0x93

I can't help noticing that this started immediately after commit
0eea804 "pg_dump: Reduce use of global variables". No idea why
the issue is only showing up on this one animal.

regards, tom lane