Update OpenMP/OpenACC analysis passes

[ouankou]

Currently, the analysis is mainly based on the original OpenMP AST construction in ROSE. There are 7 passes in the following order:

1. Convert metadirective to if statement with OpenMP variants.
2. Patch implicit private variables.
3. Patch implicit firstprivate variables.
4. Patch implicit map variables.
5. Patch task variables.
6. Create UPIR data fields based on map clauses.
7. Normalize UPIR loops.

Pass 1, 5 and 6 are OpenMP-only. The rest passes could also apply to OpenACC. Currently, the OpenACC AST constructor directly creates UPIR data fields instead of map clause. Therefore, to let OpenACC reuse passes 2-4, we should move passes 5 and 6 right after pass 1. Then all the rest passes are applied to UPIR nodes with according changes.

When the OpenACC AST constructor is fully implemented, we can copy the code handling data mapping to the OpenMP AST constructor and generate UPIR data fields directly. After that, pass 6 could be removed.