message: [tf2xla] Align sign with TensorFlow
  tf.sign(NaN) should be NaN via XLA to match TensorFlow's normal behavior.
diff: @@ -85,21 +85,8 @@ XLAJIT_MAKE_UNARY(Rsqrt, xla::Rsqrt(x));
  XLAJIT_MAKE_UNARY(Sigmoid, xla::Logistic(x));
  -// Returns 0 if x is NaN, 0 if x is 0, -1 if x < 0 and 1 if x > 0.
  -static xla::XlaOp Sign(xla::XlaBuilder* b, xla::XlaOp x) {
  - return b->ReportErrorOrReturn([&]() -> xla::StatusOr<xla::XlaOp> {
  - TF_ASSIGN_OR_RETURN(auto shape, b->GetShape(x));
  - if (xla::primitive_util::IsComplexType(shape.element_type())) {
  - return xla::Sign(x);
  - }
  - auto gt = xla::Gt(x, xla::ZerosLike(x));
  - auto lt = xla::Lt(x, xla::ZerosLike(x));
  - return xla::ConvertElementType(gt, shape.element_type()) -
  - xla::ConvertElementType(lt, shape.element_type());
  - });
  -}
  -
  -XLAJIT_MAKE_UNARY(Sign, Sign(b, x));
  +// Returns NaN if x is NaN, 0 if x is 0, -1 if x < 0 and 1 if x > 0.
  +XLAJIT_MAKE_UNARY(Sign, xla::Sign(x));
  XLAJIT_MAKE_UNARY(Sinh, xla::Sinh(x));
  static xla::XlaOp Softplus(xla::XlaBuilder* b, xla::XlaOp features) {
  