message: Better guard __builtin_clz()
diff: @@ -22,10 +22,12 @@ inline unsigned clz(unsigned val)
  {
  #if defined(__CUDA_ARCH__) && __CUDA_ARCH__ >= 200
  return __clz(val);
  +#elif defined(__GNUCC__) || (defined(__clang__) && __has_builtin(__builtin_clz))
  + return __builtin_clz(val);
  #elif defined(_WIN32)
  return __lzcnt(val);
  #else
  - return __builtin_clz(val);
  + // TODO
  #endif
  }
  