Py_DECREF: only pass filename if Py_REF_DEBUG is defined (GH-17870)

Filename and line numbers are not needed when Py_REF_DEBUG are not
defined.

The static inline _Py_DECREF() function was introduced by
commit 2aaf0c1204.

Include/object.h

@@ -461,11 +461,12 @@ static inline void _Py_INCREF(PyObject *op)
 
 #define Py_INCREF(op) _Py_INCREF(_PyObject_CAST(op))
 
-static inline void _Py_DECREF(const char *filename, int lineno,
-                              PyObject *op)
+static inline void _Py_DECREF(
+#ifdef Py_REF_DEBUG
+    const char *filename, int lineno,
+#endif
+    PyObject *op)
 {
-    (void)filename; /* may be unused, shut up -Wunused-parameter */
-    (void)lineno; /* may be unused, shut up -Wunused-parameter */
     _Py_DEC_REFTOTAL;
     if (--op->ob_refcnt != 0) {
 #ifdef Py_REF_DEBUG
@@ -479,7 +480,11 @@ static inline void _Py_DECREF(const char *filename, int lineno,
     }
 }
 
-#define Py_DECREF(op) _Py_DECREF(__FILE__, __LINE__, _PyObject_CAST(op))
+#ifdef Py_REF_DEBUG
+#  define Py_DECREF(op) _Py_DECREF(__FILE__, __LINE__, _PyObject_CAST(op))
+#else
+#  define Py_DECREF(op) _Py_DECREF(_PyObject_CAST(op))
+#endif
 
 
 /* Safely decref `op` and set `op` to NULL, especially useful in tp_clear