With C++17, compile error because of function return type incompatibility

[agcapps]

With MSVC and C++17, a user compiling an application that calls Tribol and Axom ran into this:

'axom::slam::OrderedSet<int,int,axom::slam::policies::RuntimeSize<IntType>,axom::slam::policies::RuntimeOffset<IntType>,axom::slam::policies::StrideOne<IntType>,axom::slam::policies::detail::IndexedIndirection<axom::slam::policies::CArrayIndirectionBase<tribol::IndexType,const tribol::IndexType>>,axom::slam::policies::NoSubset,axom::slam::policies::VirtualInterface>::at': 

overriding virtual function return type differs and is not covariant from

'axom::slam::Set<axom::slam::DefaultPositionType,axom::slam::DefaultElementType>::at'

d:\path\to\axom\src\axom\slam\OrderedSet.hpp    477