Add strerror to pg_dump error messages where missing.

src/bin/pg_dump/common.c

src/bin/pg_dump/pg_backup_archiver.c

src/bin/pg_dump/pg_backup_custom.c

src/bin/pg_dump/pg_backup_files.c

src/bin/pg_dump/pg_backup_tar.c

src/bin/pg_dump/pg_dumpall.c