[libc] Add new libc

This new libc is mostly from scratch, with *printf() functions provided
by Marco Paland and Eyal Rozenberg's tiny printf library, and malloc and
friends provided by dlmalloc.

src/include/arch/amd64/memory.h

@@ -2,6 +2,7 @@
 /// \file arch/amd64/memory.h
 /// Architecture-specific constants related to memory and paging
 
+#include <stddef.h>
 #include <stdint.h>
 
 namespace arch {