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/sys/debug.h

@@ -42,6 +42,19 @@ extern "C" {
     void debug_printf(
         const char *format,
         ...);
+    BACNET_STACK_EXPORT
+    int debug_aprintf(
+        const char *format,
+        ...);
+    BACNET_STACK_EXPORT
+    int debug_fprintf(
+        FILE *stream,
+        const char *format,
+        ...);
+    BACNET_STACK_EXPORT
+    void debug_perror(
+        const char *format,
+        ...);
 #if DEBUG_ENABLED
     /* Nothing more here */
 #else