Libraries: Create top level directory for libraries.

Things were getting a little crowded in the project root, so this patch
moves the Lib*/ directories into Libraries/.

Libraries/LibC/poll.cpp

@@ -0,0 +1,12 @@
+#include <Kernel/Syscall.h>
+#include <errno.h>
+#include <poll.h>
+
+extern "C" {
+
+int poll(struct pollfd* fds, int nfds, int timeout)
+{
+    int rc = syscall(SC_poll, fds, nfds, timeout);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+}