Register internal 'swig_runtime_data_type_pointer' constant as
"CONST_PERSISTENT" to avoid segmentation fault on module unload. Fixes
https://github.com/swig/swig/issues/859 reported by Timotheus Pokorra -
thanks also to Javier Torres for a minimal reproducer.
PHP5's C extension API has changed substantially so you need to use
-php7 to specify you want PHP7 compatible wrappers.
Fixes https://github.com/swig/swig/issues/571