Usage of nested parallel regions were not working correctly and leading
to assertion failures. Fix contains the following changes,
1) Don't set the insertion point in the body callback.
2) Save the continuation IP in a stack and set the branch to
continuationIP at the terminator.
Reviewed By: SouraVX, jdoerfert, ftynse
Differential Revision: https://reviews.llvm.org/D88720
a71a0d6d21