start writing STDC functions that are necessary for correct linking.

gcc will optimise calls to these four functions, and requires
definitions to these funcitons.
It is better to let it make these optimisations, rather than disabling
this functionality with the `-nostdc` flag.

src/atrb.h

@@ -0,0 +1,4 @@
+#pragma once
+#if defined(__cplusplus)
+#define restrict __restrict__
+#endif

src/string.c

@@ -0,0 +1,10 @@
+#include "string.h"
+
+int   memcmp(const void *s1, const void *s2, usize n) {
+}
+
+void *memset(void *s, int c, usize n) { }
+
+void *memcpy(void *restrict dst, const void *restrict src, usize n) { }
+
+void *memmove(void *dst, const void *src, usize n) { }

src/string.h

@@ -0,0 +1,8 @@
+#pragma once
+#include "types.h"
+#include "atrb.h"
+
+int   memcmp(const void *s1, const void *s2, usize n);
+void *memset(void *s, int c, usize n);
+void *memcpy(void *restrict dst, const void *restrict src, usize n);
+void *memmove(void *dst, const void *src, usize n);