Turn on floating point exception trapping for GCC in tests

Some simulations trap floating point exceptions to ensure that their code is working correctly, and we want VTK-m to work correctly in their code. To check this, we want to turn on floating point exception trapping in our test code. This is very implementation-specific, so for now we are just turning it on for GCC. This will at least alert a problem on some of the dashboards.

Also fix several issues where VTK-m was raising floating point exceptions.

Fixes #600 (closed)