Fix issue with Intel compiler removing loop in MatrixTranspose

For some reason when optimization was on with the Intel compiler it
was removing the loop in some instances of the templated MatrixTranspose
function. I inserted an empty assembly statement that prevents the
compiler from removing the loop but does not add any actual code. That
seems to fix the problem.

vtkm/Matrix.h

@@ -244,6 +244,15 @@ vtkm::Matrix<T,NumCols,NumRows> MatrixTranspose(
   for (vtkm::IdComponent index = 0; index < NumRows; index++)
   {
     vtkm::MatrixSetColumn(result, index, vtkm::MatrixGetRow(matrix, index));
+#ifdef VTKM_ICC
+    // For reasons I do not really understand, the Intel compiler with with
+    // optimization on is sometimes removing this for loop. It appears that the
+    // optimizer sometimes does not recognize that the MatrixSetColumn function
+    // has side effects. I cannot fathom any reason for this other than a bug in
+    // the compiler, but unfortunately I do not know a reliable way to
+    // demonstrate the problem.
+    __asm__("");
+#endif
   }
   return result;
 }