[flang] [llvm] [Flang][OMP]Add support for DECLARE MAPPER parsing and semantics (PR #115160)

[Mats Petersson via llvm-commits]

Leporacanthicus wrote:

> There are some restrictions on the DECLARE MAPPER directive that are not checked anywhere. For example, the type can't be intrinsic or abstract. Could you add them?

This is now implemented, at least for the abstract (already checked elsewhere) and "not derived" cases. 

https://github.com/llvm/llvm-project/pull/115160