[OpenMP][FIX] Consistently use OpenMPIRBuilder if requested

When we use the OpenMPIRBuilder for the parallel region we need to also
use it to get the thread ID (among other things) in the body. This is
because CGOpenMPRuntime::getThreadID() and
CGOpenMPRuntime::emitUpdateLocation implicitly assumes that if they are
called from within a parallel region there is a certain structure to the
code and certain members of the OMPRegionInfo are initialized. It might
make sense to initialize them even if we use the OpenMPIRBuilder but we
would preferably get rid of such state instead.

Bug reported by Anchu Rajendran Sudhakumari.

Depends on D82470.

Reviewed By: anchu-rajendran

Differential Revision: https://reviews.llvm.org/D82822