fix undefined pointer comparison in wmemmove

src/string/wmemmove.c

 #include <wchar.h>
+#include <stdint.h>
 
 wchar_t *wmemmove(wchar_t *d, const wchar_t *s, size_t n)
 {
 	wchar_t *d0 = d;
-	if ((size_t)(d-s) < n)
+	if ((uintptr_t)d-(uintptr_t)s < n * sizeof *d)
 		while (n--) d[n] = s[n];
 	else
 		while (n--) *d++ = *s++;