Export php_gd_libgdimageptr_from_zval_p()

Some extension may need to retrieve the `gdImagePtr` from an `GdImage`
object; thus, we export the respective function.  To not being forced
to include gd.h in php_gd.h, we use the opaque `struct gdImageStruct *`
as return type.

Author: cmb69

ext/gd/gd.c

@@ -178,7 +178,7 @@ static zend_always_inline php_gd_image_object* php_gd_exgdimage_from_zobj_p(zend
  * Converts an extension GdImage instance contained within a zval into the gdImagePtr
  * for use with library APIs
  */
-static zend_always_inline gdImagePtr php_gd_libgdimageptr_from_zval_p(zval* zp)
+inline gdImagePtr php_gd_libgdimageptr_from_zval_p(zval* zp)
 {
 	return php_gd_exgdimage_from_zobj_p(Z_OBJ_P(zp))->image;
 }

ext/gd/php_gd.h

@@ -77,6 +77,8 @@ PHP_MINIT_FUNCTION(gd);
 PHP_MSHUTDOWN_FUNCTION(gd);
 PHP_RSHUTDOWN_FUNCTION(gd);
 
+PHP_GD_API struct gdImageStruct *php_gd_libgdimageptr_from_zval_p(zval* zp);
+
 #else
 
 #define phpext_gd_ptr NULL