implement basic string functions (memset, memcpy, etc)

include/string.h

@@ -0,0 +1,12 @@
+#ifndef STRING_H
+#define STRING_H
+
+#include <stddef.h>
+
+int memcmp(const void*, const void*, size_t);
+void* memcpy(void* __restrict, const void* __restrict, size_t);
+void* memmove(void*, const void*, size_t);
+void* memset(void*, int, size_t);
+size_t strlen(const char*);
+
+#endif