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/ms-input.c

@@ -140,6 +140,7 @@ bool Multistate_Input_Valid_Instance(uint32_t object_instance)
 
 static uint32_t Multistate_Input_Max_States(uint32_t instance)
 {
+    (void)instance;
     return MULTISTATE_NUMBER_OF_STATES;
 }