BUG #16568: pg_upgrade failed from 9.3 to 9.6

The following bug has been logged on the website:

Bug reference: 16568
Logged by: Phanindra A
Email address: a(dot)h(dot)s(dot)phani(at)gmail(dot)com
PostgreSQL version: 9.6.18
Operating system: rhel 6.7
Description:

Hi,
I am trying to upgrade PG 9.3.4 (repmgr 3.0.1) to PG 9.6.18 (repmgr 4.4)
. On using pg_upgrade getting below error.
$ /usr/local/pgsql-9.6/bin/pg_upgrade -b /usr/local/pgsql/bin -B
/usr/local/pgsql-9.6/bin -d /pgdata/data/ -D /pgdata/data_9.6 -U postgres
-c

*failure*
Consult the last few lines of "pg_upgrade_server.log" for
the probable cause of the failure.
Performing Consistency Checks on Old Live Server
------------------------------------------------
Checking cluster versions ok
Checking database user is the install user ok
Checking database connection settings ok
Checking for prepared transactions ok
Checking for reg* system OID user data types ok
Checking for contrib/isn with bigint-passing mismatch ok
Checking for roles starting with 'pg_' ok
Checking for invalid "line" user columns ok
Checking for presence of required libraries fatal

Your installation references loadable libraries that are missing from the
new installation. You can add these libraries to the new installation,
or remove the functions using them from the old installation. A list of
problem libraries is in the file:
loadable_libraries.txt

Failure, exiting
$ cat loadable_libraries.txt

could not load library "$libdir/repmgr_funcs":
ERROR: could not access file "$libdir/repmgr_funcs": No such file or
directory

$ pg_config --pkglibdir
/usr/local/pgsql/lib
$ ll /usr/local/pgsql/lib/repmgr_funcs.so
-rwxrwxrwx. 1 root root 10220 Mar 27 2018
/usr/local/pgsql/lib/repmgr_funcs.so

Repmgr installation is done form source.

postgres configuration is done like below.
$ grep shared_preload_libraries /pgdata/data/postgresql.conf
shared_preload_libraries = 'repmgr_funcs' # (change requires
restart)
$ grep shared_preload_libraries /pgdata/data_9.6/postgresql.conf
shared_preload_libraries = 'repmgr' # (change requires restart)