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/scanf_impl.h

@@ -0,0 +1,5 @@
+#pragma once
+
+#include <stdarg.h>
+
+int scanf_impl(const char* format, va_list arguments, int (*getc_fun)(void*), void* data);