BuildSystem: Move all userpace libraries under the userspace directory

As the number of libraries is increasing, root directory starts to
expand. This adds better organization for libraries

userspace/libraries/LibC/include/sys/msg.h

@@ -0,0 +1,42 @@
+#ifndef _SYS_MSG_H
+#define _SYS_MSG_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_msg.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#define __need_pid_t
+#define __need_size_t
+#define __need_ssize_t
+#define __need_time_t
+#include <sys/types.h>
+
+#include <sys/ipc.h>
+
+typedef unsigned int msgqnum_t;
+typedef unsigned int msglen_t;
+
+#define MSG_NOERROR 0
+
+struct msqid_ds
+{
+	struct ipc_perm	msg_perm;	/* Operation permission structure. */
+	msgqnum_t		msg_qnum;	/* Number of messages currently on queue. */
+	msglen_t		msg_qbytes;	/* Maximum number of bytes allowed on queue. */
+	pid_t			msg_lspid;	/* Process ID of last msgsnd(). */
+	pid_t			msg_lrpid;	/* Process ID of last msgrcv(). */
+	time_t			msg_stime;	/* Time of last msgsnd(). */
+	time_t			msg_rtime;	/* Time of last msgrcv(). */
+	time_t			msg_ctime;	/* Time of last change. */
+};
+
+int			msgctl(int msqid, int cmd, struct msqid_ds* buf);
+int			msgget(key_t key, int msgflg);
+ssize_t		msgrcv(int msqid, void* msgp, size_t msgsz, long msgtyp, int msgflg);
+int			msgsnd(int msqid, const void* msgp, size_t msgsz, int msgflg);
+
+__END_DECLS
+
+#endif