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/select.h

@@ -0,0 +1,66 @@
+#ifndef _SYS_SELECT_H
+#define _SYS_SELECT_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_select.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#include <bits/types/timeval.h>
+
+#include <signal.h>
+#include <time.h>
+
+#define FD_SETSIZE 1024
+
+typedef unsigned long __fd_mask;
+#define __FD_MASK_SIZE (8 * sizeof(__fd_mask))
+
+typedef struct {
+	__fd_mask __bits[FD_SETSIZE / __FD_MASK_SIZE];
+} fd_set;
+
+#define FD_CLR(fd, setp) \
+	do { \
+		__fd_mask off = (fd) / __FD_MASK_SIZE; \
+		__fd_mask bit = (fd) % __FD_MASK_SIZE; \
+		(setp)->__bits[off] &= ~((__fd_mask)1 << bit); \
+	} while (0)
+
+#define FD_ISSET(fd, setp) \
+	({ \
+		__fd_mask off = (fd) / __FD_MASK_SIZE; \
+		__fd_mask bit = (fd) % __FD_MASK_SIZE; \
+		(setp)->__bits[off] & ((__fd_mask)1 << bit); \
+	})
+
+#define FD_SET(fd, setp) \
+	do { \
+		__fd_mask off = (fd) / __FD_MASK_SIZE; \
+		__fd_mask bit = (fd) % __FD_MASK_SIZE; \
+		(setp)->__bits[off] |= ((__fd_mask)1 << bit); \
+	} while (0)
+
+#define FD_ZERO(setp) \
+	do { \
+		for (int i = 0; i < FD_SETSIZE / __FD_MASK_SIZE; i++) \
+			(setp)->__bits[i] = (__fd_mask)0; \
+	} while (0)
+
+struct sys_pselect_t
+{
+	int nfds;
+	fd_set* readfds;
+	fd_set* writefds;
+	fd_set* errorfds;
+	const struct timespec* timeout;
+	const sigset_t* sigmask;
+};
+
+int pselect(int nfds, fd_set* __restrict readfds, fd_set* __restrict writefds, fd_set* __restrict errorfds, const struct timespec* __restrict timeout, const sigset_t* __restrict sigmask);
+int select(int nfds, fd_set* __restrict readfds, fd_set* __restrict writefds, fd_set* __restrict errorfds, struct timeval* __restrict timeout);
+
+__END_DECLS
+
+#endif