fix arm compilation (PR 694)

src/prim/unix/prim.c

@@ -759,7 +759,7 @@ bool _mi_prim_random_buf(void* buf, size_t buf_len) {
       ssize_t ret = syscall(SYS_getrandom, buf, buf_len, GRND_NONBLOCK);
       if (ret >= 0) return (buf_len == (size_t)ret);
       if (errno != ENOSYS) return false;
-      mi_atomic_store_release(&no_getrandom, 1UL); // don't call again, and fall back to /dev/urandom
+      mi_atomic_store_release(&no_getrandom, (uintptr_t)1); // don't call again, and fall back to /dev/urandom
     }
   #endif
   int flags = O_RDONLY;