Workaround for the CCE 17 requiring explicit copy for reduction variables...

Workaround for the CCE 17 requiring explicit copy for reduction variables (!99)

CCE 17 needed for AMD GPUs on LUMI now requires an explicit copy of reduction variables.
Add copy clauses for the reduction variables.

Approved-by: Yen-Chen Chen <yen-chen.chen@kit.edu>
Merged-by: Yen-Chen Chen <yen-chen.chen@kit.edu>
Changelog: bugfix