__GNUC__ does not imply gcc version is present, so just check for version (closes #14994)

Include/pyerrors.h

@@ -87,7 +87,7 @@ PyAPI_FUNC(void) PyErr_GetExcInfo(PyObject **, PyObject **, PyObject **);
 PyAPI_FUNC(void) PyErr_SetExcInfo(PyObject *, PyObject *, PyObject *);
 
 #if defined(__clang__) || \
-    (defined(__GNUC__) && \
+    (defined(__GNUC_MAJOR__) && \
      ((__GNUC_MAJOR__ >= 3) || \
       (__GNUC_MAJOR__ == 2) && (__GNUC_MINOR__ >= 5)))
 #define _Py_NO_RETURN __attribute__((__noreturn__))