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/uio.h

@@ -0,0 +1,25 @@
+#ifndef _SYS_UIO_H
+#define _SYS_UIO_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_uio.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#define __need_size_t
+#define __need_ssize_t
+#include <sys/types.h>
+
+struct iovec
+{
+	void*	iov_base;	/* Base address of a memory region for input or output. */
+	size_t	iov_len;	/* The size of the memory pointed to by iov_base. */
+};
+
+ssize_t readv(int fildes, const struct iovec* iov, int iovcnt);
+ssize_t writev(int fildes, const struct iovec* iov, int iovcnt);
+
+__END_DECLS
+
+#endif