This patch adds support for omp task to the OpenMPIRBuilder. To
simplify this *and* to make optimizations of tasks possible, we
introduce a new interface: __kmpc_task.
Similar to TRegions, the new interface exposes front-end information in
a direct way. More importantly, the task create and task issue step are
conceptually not separated anymore as it is, together with other
non-user related code, hidden inside __kmpc_task.
Most of the properties of a task are supported already, incl. dependences.
The outlining logic used for omp parallel was (slightly) generalized
and reused but better abstractions are needed.