PostgreSQL upgrade via pg_upgrade fails when using Red Hat Software Collections (RHSCL)

Issue

PostgreSQL upgrade via pg_upgrade fails when using packages provided by Red Hat Software Collections (RHSCL).

For example, command for upgrading from Postgresql-9.6 to Postgresql-10 (both are provided by RHSCL) when run from PostgreSQL-10 RHSCL environment:

$  pg_upgrade --old-datadir=/db/pgdata/96 --new-datadir=/db/pgdata/10 --old-bindir=/opt/rh/rh-postgresql96/root/bin  --new-bindir=/opt/rh/rh-postgresql10/root/bin  --check

could not get pg_ctl version data using "/opt/rh/rh-postgresql96/root/bin/pg_ctl" --version: Success
Failure, exiting

Similar command when run from PostgreSQL-9.6 RHSCL environment:

$  pg_upgrade --old-datadir=/db/pgdata/96 --new-datadir=/db/pgdata/10 --old-bindir=/opt/rh/rh-postgresql96/root/bin  --new-bindir=/opt/rh/rh-postgresql10/root/bin  --check

check for "/opt/rh/rh-postgresql10/root/bin/pg_resetxlog" failed: No such file or directory
Failure, exiting