[flang] [llvm] [flang][cuda] Fix device-variable leaks and reset-safe cleanup (PR #209865)

[via llvm-commits]

https://github.com/jeanPerier commented:

Mostly LGTM, just a question about placing Fortran finalization of device variables under "CUFDeviceIsActive" runtime condition.

https://github.com/llvm/llvm-project/pull/209865