Remove undefined behaviors

libc/str/memchr.c

@@ -31,7 +31,7 @@ void *memchr(const void *m, int c, size_t n) {
   uint64_t v, w;
   const char *p, *pe;
   c &= 255;
-  v = 0x0101010101010101 * c;
+  v = 0x0101010101010101ul * c;
   for (p = m, pe = p + n; p + 8 <= pe; p += 8) {
     w = (uint64_t)(255 & p[7]) << 070 | (uint64_t)(255 & p[6]) << 060 |
         (uint64_t)(255 & p[5]) << 050 | (uint64_t)(255 & p[4]) << 040 |