1. In header-only mode, non-explicit conversion functions between
DIY_MPI_..., MPI_... and diy::mpi... types are available. So passing MPI types
directly where DIY_MPI... types are expected should work.

2. In library mode, use `mpi_cast` to convert from diy to mpi types and
`make_DIY_MPI..` to convert from mpi to diy handle types.

3. In code that is expected to work in both header-only and library
modes, method 2 above should be used. This includes all code that is
part of the diy library.

Enable stricter warnings that are used by client projects like VTK-m, so that
they are caught sooner.

This will reduce the number of backported changes from VTK-m.

Robert Maynard authored 5 years ago and Sujin Philip committed 5 years ago

This uses a more robust set of checks to determine if
std::is_trivially_copyable exist given the libstdc++ version value

In pick.hpp, in() was calling wrap_bounds() with old arguments. Removed
the last argument, link.dimension().

Help compiler not get confused about save/load overloads for default
arguments (C2440).