This generates a warning with PHP 7.3 which apparently will become an error in the future. We're just checking that a constant that should not be define indeed isn't, which we can achieve more cleanly using get_defined_constants() instead.
git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@10967 626c5289-ae23-0410-ae9c-e8d60b6d4f22