Add support for "omp cancel taskgroup" to the OmpCluster graph integration

Summary

Add support for task cancellation to OmpCluster task graph integration.

Description

The taskgroup and cancel taskgroup clauses can be used to implement iterative applications where its execution is halted once the result reaches a pre-determined accuracy metric. The current integration of OmpCluster with OpenMP task graph did not account for a task graph to be cancelled and assume that all the graph tasks would be executed. We should fix this behavior, which would lead to the correct execution of such applications, e.g. BESO.

Possible comparisons

No difference in the execution should be noticed.

Tasks

• Add support for on demand task graph updates.
• Add warnings about cancelled tasks (useful for inner testing).
• Avoid static initialization/de-initialization fiasco in the task graph integration context.

New tests

A new test must be added to check the integration between omp cancel taskgroup and the OmpCluster plugin.