dbgutil.h: extern "C" for C++

tests/dbgutil.h

@@ -19,6 +19,10 @@
 
 #include "quirc.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* Dump decoded information on stdout. */
 void dump_data(const struct quirc_data *data);
 
@@ -45,4 +49,8 @@ int check_if_png(const char *filename);
  */
 int load_png(struct quirc *q, const char *filename);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif