Cleanup follow up to
   r14-1579-g4ede915d5dde93 "openmp: Add support for the 'present' modifier"
committed 6 days ago.

Namely:
* Replace for the program → libgomp ABI GOMP_MAP_PRESENT_[ALLOC,TO,FROM,TOFROM]
   by the preexisting GOMP_MAP_FORCE_PRESENT but keep the other enum values
   (and use them until gimplifcation).

* Improve wording if a non-existing/unsupported map-type modifier was used
   by not referring to 'omp target' as it could be also target (enter/exit) data.
   + Add a testcase for enter/exit data + data.

* Unify + improve wording shown for 'present' when not present on the device.

* Extend in the testcases to check that data actually gets copied with
   'target update' and 'map when the 'present' modifier is present.

Committed as Rev. r14-1736-g38944ec2a6fa10

Tobias
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