[OpenMP] Add support for CPU offloading in new driver

This patch adds support for linking CPU offloading applications in the
linker wrapper. We generate the necessary linking job using the host
linker's path and library arguments. This may not be true for more
complex offloading schemes, but this is sufficient for now.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D119613