Fix Makefile spurious rebuilds

Add mem* functions to stdio
Add constant int functions

include/bits/string.h

@@ -0,0 +1,9 @@
+#ifndef _BITS_STDIO_H
+#define _BITS_STDIO_H
+
+int memcmp(const void *s1, const void *s2, size_t n);
+void *memcpy(void *dest, const void *src, size_t n);
+void *memmove(void *dest, const void *src, size_t n);
+void *memset(void *s, int c, size_t n);
+
+#endif /* _BITS_STDIO_H */