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/piv.c

@@ -140,11 +140,13 @@ bool PositiveInteger_Value_Present_Value_Set(
     unsigned index = 0;
     bool status = false;
 
+    (void)priority;
     index = PositiveInteger_Value_Instance_To_Index(object_instance);
     if (index < MAX_POSITIVEINTEGER_VALUES) {
         PIV_Descr[index].Present_Value = value;
         status = true;
     }
+
     return status;
 }
 
@@ -359,4 +361,5 @@ bool PositiveInteger_Value_Write_Property(BACNET_WRITE_PROPERTY_DATA *wp_data)
 
 void PositiveInteger_Value_Intrinsic_Reporting(uint32_t object_instance)
 {
+    (void)object_instance;
 }