[PHP] Add support for PHP7.

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

Examples/php5/check.list

@@ -0,0 +1,19 @@
+# see top-level Makefile.in
+# (see also top-level configure.ac kludge)
+callback
+class
+constants
+cpointer
+disown
+enum
+extend
+funcptr
+overloading
+pointer
+pragmas
+proxy
+reference
+simple
+sync
+value
+variables