LibIPC: Add missing errno.h include

Author: https://github.com/boricj
Commit: 9aa44fa36c
Pull-request: https://github.com/SerenityOS/serenity/pull/6671
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibIPC/Connection.h

@@ -14,6 +14,7 @@
 #include <LibCore/Notifier.h>
 #include <LibCore/Timer.h>
 #include <LibIPC/Message.h>
+#include <errno.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>