nvcc warnings

[adayton1]

I was able to build the develop branch of Axom successfully with nvcc 12.9.1. However, there are a number of warnings like the following:

axom/src/axom/core/../../axom/core/FlatMapView.hpp(49): warning #20012-D: __host__ annotation is ignored on a function("FlatMapView") that is explicitly defaulted on its first declaration
    __attribute__((host)) __attribute__((device)) FlatMapView() = default;
                   ^

Remark: The warnings can be suppressed with "-diag-suppress <warning-number>"

I think this can be fixed by changing AXOM_HOST_DEVICE FlatMapView() = default; to just FlatMapView() = default;. The compiler can still generate both host and device versions of a defaulted constructor.

[BradWhitlock]

I fixed this specific warning in PR #1796 .

[rhornung67]

Check that these warnings are squashed before closing this issue