thr_alarm.c, thr_lock.c, my_global.h:

  Avoid multiple define of DBUG_OFF (bug#21749)

include/my_global.h

@@ -614,12 +614,17 @@ C_MODE_END
 #define _STATIC_VARARGS(X) X
 #define _PC(X)	X
 
+/* The DBUG_ON flag always takes precedence over default DBUG_OFF */
 #if defined(DBUG_ON) && defined(DBUG_OFF)
 #undef DBUG_OFF
 #endif
 
-#if defined(_lint) && !defined(DBUG_OFF)
-#define DBUG_OFF
+/* We might be forced to turn debug off, if not turned off already */
+#if (defined(FORCE_DBUG_OFF) || defined(_lint)) && !defined(DBUG_OFF)
+#  define DBUG_OFF
+#  ifdef DBUG_ON
+#    undef DBUG_ON
+#  endif
 #endif
 
 #include <my_dbug.h>

mysys/thr_alarm.c

@@ -15,8 +15,7 @@
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 
 /* To avoid problems with alarms in debug code, we disable DBUG here */
-#undef DBUG_OFF
-#define DBUG_OFF
+#define FORCE_DBUG_OFF
 #include <my_global.h>
 
 #if defined(THREAD) && !defined(DONT_USE_THR_ALARM)

mysys/thr_lock.c

@@ -72,7 +72,7 @@ multiple read locks.
 */
 
 #if !defined(MAIN) && !defined(DBUG_OFF) && !defined(EXTRA_DEBUG)
-#define DBUG_OFF
+#define FORCE_DBUG_OFF
 #endif
 
 #include "mysys_priv.h"