[OpenMP][FIX] Query proper thread ID information to support nesting

The OpenMP thread ID is not the hardware thread ID if we have nesting.
We need to ask the runtime properly to ensure correct results.

Note that the loop interface is going to change soon so we do not adjust
it now but simply ignore the extra argument.

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D111950