Fix debug messages shown even from disabled levels

Messages from ENTERFUNC and RETURNFUNC where stored in an internal buffer
even whe debug_level wasn't TRACE and were returned when calling rigerror().

include/hamlib/rig.h

@@ -3770,11 +3770,10 @@ extern HAMLIB_EXPORT_VAR(char) debugmsgsave2[DEBUGMSGSAVE_SIZE];  // last-1 debu
 // debugmsgsave3 is deprecated
 extern HAMLIB_EXPORT_VAR(char) debugmsgsave3[DEBUGMSGSAVE_SIZE];  // last-2 debug msg
 #define rig_debug_clear() { debugmsgsave[0] = debugmsgsave2[0] = debugmsgsave3[0] = 0; };
-#ifndef __cplusplus
-#ifdef __GNUC__
-// doing the debug macro with a dummy sprintf allows gcc to check the format string
-#define rig_debug(debug_level,fmt,...) do { snprintf(debugmsgsave2,sizeof(debugmsgsave2),fmt,__VA_ARGS__);rig_debug(debug_level,fmt,##__VA_ARGS__); add2debugmsgsave(debugmsgsave2); } while(0)
-#endif
+#if !defined(__cplusplus) && defined(__GNUC__)
+#define ATTRIBUTE_FORMAT_PRINTF __attribute__((__format__ (__printf__, 2, 3)))
+#else
+#define ATTRIBUTE_FORMAT_PRINTF
 #endif
 
 // Measuring elapsed time -- local variable inside function when macro is used
@@ -3786,7 +3785,7 @@ extern HAMLIB_EXPORT_VAR(char) debugmsgsave3[DEBUGMSGSAVE_SIZE];  // last-2 debu
 
 extern HAMLIB_EXPORT(void)
 rig_debug HAMLIB_PARAMS((enum rig_debug_level_e debug_level,
-                         const char *fmt, ...));
+                         const char *fmt, ...)) ATTRIBUTE_FORMAT_PRINTF;
 
 extern HAMLIB_EXPORT(vprintf_cb_t)
 rig_set_debug_callback HAMLIB_PARAMS((vprintf_cb_t cb,

src/debug.c

@@ -202,7 +202,6 @@ void HAMLIB_API rig_set_debug_time_stamp(int flag)
  * The formatted character string is passed to the `vfprintf`(3) C library
  * call and follows its format specification.
  */
-#undef rig_debug
 void HAMLIB_API rig_debug(enum rig_debug_level_e debug_level,
                           const char *fmt, ...)
 {