message: build: eliminate warnings
  warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
diff: @@ -1483,14 +1483,14 @@ double cv::threshold( InputArray _src, OutputArray _dst, double thresh, double m
  imaxval = saturate_cast<ushort>(imaxval);
  int ushrt_min = 0;
  - if (ithresh < ushrt_min || ithresh >= USHRT_MAX)
  + if (ithresh < ushrt_min || ithresh >= (int)USHRT_MAX)
  {
  if (type == THRESH_BINARY || type == THRESH_BINARY_INV ||
  ((type == THRESH_TRUNC || type == THRESH_TOZERO_INV) && ithresh < ushrt_min) ||
  - (type == THRESH_TOZERO && ithresh >= USHRT_MAX))
  + (type == THRESH_TOZERO && ithresh >= (int)USHRT_MAX))
  {
  - int v = type == THRESH_BINARY ? (ithresh >= USHRT_MAX ? 0 : imaxval) :
  - type == THRESH_BINARY_INV ? (ithresh >= USHRT_MAX ? imaxval : 0) :
  + int v = type == THRESH_BINARY ? (ithresh >= (int)USHRT_MAX ? 0 : imaxval) :
  + type == THRESH_BINARY_INV ? (ithresh >= (int)USHRT_MAX ? imaxval : 0) :
  /*type == THRESH_TRUNC ? imaxval :*/ 0;
  dst.setTo(v);
  }
  