[libc] Remove old libc

Removing the very old PDCLib-based libc, in preparation for adding the
new one.

src/libraries/libc/stdalign.h

@@ -1,14 +0,0 @@
-#pragma once
-/* Alignment <stdalign.h>
-
-   This file is part of the Public Domain C Library (PDCLib).
-   Permission is granted to use, modify, and / or redistribute at will.
-*/
-
-#ifndef __cplusplus
-#define alignas _Alignas
-#define alignof _Alignof
-#endif
-
-#define __alignas_is_defined 1
-#define __alignof_is_defined 1