Fixed bug on old versions of librdkafka

kafkaada.gpr

@@ -1,5 +1,5 @@
 project KafkaAda is
-    for Languages use ("Ada");
+    for Languages use ("Ada", "C");
     for Source_Dirs use ("src/**");
     for Object_Dir use "obj";
 

src/kafka-message.ads

@@ -37,6 +37,6 @@ private
     function rd_kafka_message_errstr(Message : access constant Message_Type) return chars_ptr
         with Import => True,
              Convention => C,
-             External_Name => "rd_kafka_message_errstr";
+             External_Name => "rd_kafka_message_errstr_wrapper";
 
 end Kafka.Message;

src/wrapper.c

@@ -0,0 +1,7 @@
+
+#include <librdkafka/rdkafka.h>
+
+RD_EXPORT const char* rd_kafka_message_errstr_wrapper(const rd_kafka_message_t* rkmessage)
+{
+    return rd_kafka_message_errstr(rkmessage);
+}