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/semaphore.h

@@ -0,0 +1,30 @@
+#ifndef _SEMAPHORE_H
+#define _SEMAPHORE_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/semaphore.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#include <fcntl.h>
+#include <time.h>
+
+typedef void* sem_t;
+
+#define SEM_FAILED ((sem_t*)0)
+
+int		sem_close(sem_t* sem);
+int		sem_destroy(sem_t* sem);
+int		sem_getvalue(sem_t* __restrict sem, int* __restrict sval);
+int		sem_init(sem_t* sem, int pshared, unsigned value);
+sem_t*	sem_open(const char* name, int oflag, ...);
+int		sem_post(sem_t* sem);
+int		sem_timedwait(sem_t* __restrict sem, const struct timespec* __restrict abstime);
+int		sem_trywait(sem_t* sem);
+int		sem_unlink(const char* name);
+int		sem_wait(sem_t* sem);
+
+__END_DECLS
+
+#endif