It's 4 lines of code to implement it. So even if it is not available on a platform (glibc mmmh because of Dreppers stubborness), it's no problem.

    size_t strlcpy(char *dst, const char *src, size_t dstsize)
    {
       size_t len = strlen(src);
      if(dstsize)
        *((char*)mempcpy(dst, src, min(len, dstsize-1))) = 0;
      return len;
    }

and

     *((char*)mempcpy(dst, src, min(len, dstsize-1))) = 0;

can be replace by

     ((char*)memcpy(dst, src, min(len, dstsize-1))[min(len, dstsize-1)] = 0;

if you don't have mempcpy