Bring back set_aumessage_mode

Leave this in the ABI until 2027 to allow existing
programs to keep working. No new programs can use it.

Author: stevegrubb

common/common.h

@@ -94,8 +94,13 @@ void wall_message(const char *fmt, ...)
 
 typedef enum { MSG_STDERR, MSG_SYSLOG, MSG_QUIET } message_t;
 typedef enum { DBG_NO, DBG_YES } debug_message_t;
-void set_aumessage_mode(message_t mode, debug_message_t debug);
 
 AUDIT_HIDDEN_END
+
+// Leave this exposed until 2027, then hide it for good.
+// This allows programs already compiled to keep working.
+// But new programs can't see it.
+void set_aumessage_mode(message_t mode, debug_message_t debug);
+
 #endif