reference: use step leap mode by default if system is not supported

local.c

@@ -612,6 +612,14 @@ LCL_MakeStep(void)
 
 /* ================================================== */
 
+int
+LCL_CanSystemLeap(void)
+{
+  return drv_set_leap ? 1 : 0;
+}
+
+/* ================================================== */
+
 void
 LCL_SetSystemLeap(int leap)
 {

local.h

@@ -198,6 +198,10 @@ extern void LCL_Finalise(void);
    to a timezone problem. */
 extern int LCL_MakeStep(void);
 
+/* Check if the system driver supports leap seconds, i.e. LCL_SetSystemLeap
+   does something */
+extern int LCL_CanSystemLeap(void);
+
 /* Routine to set the system clock to correct itself for a leap second if
    supported.  Leap second will be inserted at the end of the day if the
    argument is positive, deleted if negative, and zero resets the setting. */

reference.c

@@ -240,6 +240,9 @@ REF_Initialise(void)
   leap_timer_running = 0;
   leap_in_progress = 0;
   leap_mode = CNF_GetLeapSecMode();
+  /* Switch to step mode if the system driver doesn't support leap */
+  if (leap_mode == REF_LeapModeSystem && !LCL_CanSystemLeap())
+    leap_mode = REF_LeapModeStep;
 
   leap_tzname = CNF_GetLeapSecTimezone();
   if (leap_tzname) {