Fix bfloat16 round on gcc 4.8

Eigen/src/Core/MathFunctions.h

diff --git a/Eigen/src/Core/MathFunctions.h b/Eigen/src/Core/MathFunctions.h
index 40fcb5d..a5c078b 100644
--- a/Eigen/src/Core/MathFunctions.h
+++ b/Eigen/src/Core/MathFunctions.h
@@ -407,7 +407,7 @@
     {
       EIGEN_STATIC_ASSERT((!NumTraits<Scalar>::IsComplex), NUMERIC_TYPE_MUST_BE_REAL)
       EIGEN_USING_STD_MATH(round);
-      return round(x);
+      return Scalar(round(x));
     }
   };
 #else