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/assert.h

@@ -0,0 +1,20 @@
+#ifndef __ASSERT_H
+#define _ASSERT_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/assert.h.html
+
+#include <sys/cdefs.h>
+
+#ifdef NDEBUG
+	#define assert(ignore) ((void)0)
+#else
+	#define assert(expr) ((expr) ? (void)0 : __assert_fail(#expr, __FILE__, __LINE__, __func__))
+#endif
+
+__BEGIN_DECLS
+
+[[noreturn]] void __assert_fail(const char*, const char*, int, const char*);
+
+__END_DECLS
+
+#endif