[OMPT] Handling of the events of initial-task-begin and initial-task-end

OpenMP 5.0 says that the callback for the events initial-task-begin and
initial-task-end has to be ompt_callback_implicit_task.

Patch by Tim Cramer

Differential Revision: https://reviews.llvm.org/D58776

git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@361157 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed