Bugfix/code clean using gcc warnings (#371)

* Enable extra GCC warnings to discover subtle bugs

* convert c++ comments to c comments

* cleanup pedantic compiler warnings

* Compile apps with GNU89 GNU99 GNU11 and GNU17

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

src/bacnet/basic/object/av.c

@@ -236,12 +236,14 @@ bool Analog_Value_Present_Value_Set(
     unsigned index = 0;
     bool status = false;
 
+    (void)priority;
     index = Analog_Value_Instance_To_Index(object_instance);
     if (index < MAX_ANALOG_VALUES) {
         Analog_Value_COV_Detect(index, value);
         AV_Descr[index].Present_Value = value;
         status = true;
     }
+
     return status;
 }
 
@@ -1136,6 +1138,8 @@ void Analog_Value_Intrinsic_Reporting(uint32_t object_instance)
                     CurrentAV->Event_Time_Stamps[TRANSITION_TO_NORMAL] =
                         event_data.timeStamp.value.dateTime;
                     break;
+                default:
+                    break;
             }
         }