create function updated in PostgreSQL 11.

Starting with PostgreSQL 11, the WITH(attribute) was removed from CREATE FUNCTION. If you try to install iplike into PostgreSQL 11, you get an error:

$ /usr/local/sbin/install_iplike.sh
ERROR:  syntax error at or near "WITH"
LINE 1: .../usr/local/lib/postgresql/iplike.so' LANGUAGE 'c' WITH(isstr...
                                                             ^

Documentation from PostgreSQL 9.4, 9.5, 9.6 and 10 indicate they support WITH(isStrict).

WITH(isStrict) is equivalent to STRICT or RETURNS NULL ON NULL INPUT.

Documentation from PostgreSQL 9.4, 9.5, 9.6, 10 and 11 all indicate they support STRICT or RETURNS NULL ON NULL INPUT.