+ /* On Mac OS X 10.3 or newer, we know that snprintf's return
+ value conforms to ISO C 99: the tests gl_SNPRINTF_RETVAL_C99
+ and gl_SNPRINTF_TRUNCATION_C99 pass.
+ Therefore we can avoid using %n in this situation.
+ On Mac OS X 10.13 or newer, the use of %n in format strings
+ in writable memory by default crashes the program, so we
+ should avoid it in this situation. */