py/scheduler: Add "raise_exc" argument to mp_handle_pending.

Previous behaviour is when this argument is set to "true", in which case
the function will raise any pending exception.  Setting it to "false" will
cancel any pending exception.

ports/samd/mpconfigport.h

@@ -92,8 +92,8 @@ extern const struct _mp_obj_module_t mp_module_utime;
 
 #define MICROPY_EVENT_POLL_HOOK \
     do { \
-        extern void mp_handle_pending(void); \
-        mp_handle_pending(); \
+        extern void mp_handle_pending(bool); \
+        mp_handle_pending(true); \
         __WFI(); \
     } while (0);