fixed missing types when first time compiling

Will fix the follow errors on first time compiling:
```shell
php_forp.h:71:2: error: unknown type name ‘forp_node_t’
php_forp.h:72:2: error: unknown type name ‘forp_node_t’
php_forp.h:74:2: error: unknown type name ‘forp_node_t’
php_forp.h:82:5: error: unknown type name ‘forp_var_t
```