[OpenMP] Simplify accessing num-teams and team-num

[hansangbae]

We found an issue with accessing correct number of teams and team number when the enclosing region is serialized due to use of if clause. It appears that the existing method is not able to handle such cases, so this change proposes a simpler way of accessing the team struct bound to the implicit task invoked by each OpenMP team in the league.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[jprotze]

Why is the extra team info necessary at all? There was a full team created and populated with information during creation of the league. For parallel execution, these thread data structures are used, but for a serialized team, a new data structure is used and populated with information !?!

[hansangbae]

Why is the extra team info necessary at all? There was a full team created and populated with information during creation of the league. For parallel execution, these thread data structures are used, but for a serialized team, a new data structure is used and populated with information !?!

I think invocation of serialized parallel call (__kmpc_serialized_parallel) was not considered at all when the runtime started to support teams construct. The behavior of the entry itself does not have any problem when it is invoked outside of a teams region.
Anyway, we may be able to have a better fix when clang also uses __kmpc_fork_call_if.