main: cancel clock correction before dumping sources

On exit, cancel the remaining clock correction before measurements are
saved to dumpdir to fix them for the state in which chronyd will start
again.

local.h

@@ -197,6 +197,9 @@ extern void LCL_Finalise(void);
    to a timezone problem. */
 extern int LCL_MakeStep(void);
 
+/* Routine to cancel the outstanding system clock correction */
+extern void LCL_CancelOffsetCorrection(void);
+
 /* Check if the system driver supports leap seconds, i.e. LCL_SetSystemLeap
    does something */
 extern int LCL_CanSystemLeap(void);