Export GpuDevice Globals

[ax3l]

Summary

Implement symbol export via AMREX_EXPORT for the global variables in Src/Base/AMReX_GpuDevice.H.

Additional background

Follow-up to #1847 #1847

Fix #2917

Checklist

The proposed changes:

• [x] fix a bug or incorrect behavior in AMReX
• [ ] add new capabilities to AMReX
• [ ] changes answers in the test suite to more than roundoff level
• [ ] are likely to significantly affect the results of downstream AMReX users
• [ ] include documentation in the code and/or rst files, if appropriate