Add a #if ( configUSE_TIMERS ) conditional compilation constant in to allow the software timers source file to be included in a build that is not configured to use timers without resulting in linker errors.

Source/timers.c

@@ -63,6 +63,12 @@ task.h is included from an application file. */
 
 #undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE
 
+/* This entire source file will be skipped if the application is not configured
+to include software timer functionality.  This #if is closed at the very bottom
+of this file.  If you want to include software timer functionality then ensure 
+configUSE_TIMERS is set to 1 in FreeRTOSConfig.h. */
+#if ( configUSE_TIMERS == 1 )
+
 /* Misc definitions. */
 #define tmrNO_DELAY		( portTickType ) 0U
 
@@ -621,3 +627,7 @@ xTIMER *pxTimer = ( xTIMER * ) xTimer;
 }
 /*-----------------------------------------------------------*/
 
+/* This entire source file will be skipped if the application is not configured
+to include software timer functionality.  If you want to include software timer
+functionality then ensure configUSE_TIMERS is set to 1 in FreeRTOSConfig.h. */
+#endif /* configUSE_TIMERS == 1 */