Fix include for cub::Swap
A problem we have with the vtkm::Swap method is that it can be
ambiguous with the cub::Swap method that is part of the CUDA CUB
library. We get around this problem by using the CUB version of the
function when it is available.
However, we were missing an include statement that necessarily provided
cub::Swap. This function is now explicitly provided so that we no
longer rely on including it indirectly elsewhere.
Fixes: #834 (closed)
Backport: release
Backport: release-2.1
Backport: release-2.0
Edited by Kenneth Moreland