Undef macro in TensorContractionGpu.h that causes buildbreakages.

unsupported/Eigen/CXX11/src/Tensor/TensorContractionGpu.h

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorContractionGpu.h b/unsupported/Eigen/CXX11/src/Tensor/TensorContractionGpu.h
index ea34035..780e896 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorContractionGpu.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorContractionGpu.h
@@ -1057,6 +1057,8 @@
     __syncthreads();
   }  // end loop over k
 
+#undef add_vals
+
   __syncthreads();
   Index horiz_base = (threadIdx.y / 4) * 8 + base_n;
   if (!CHECK_LHS_BOUNDARY && !CHECK_RHS_BOUNDARY) {