[OpenMP] Add better testing for the linker wrapper

The linker wrapper is used to perform linking and wrapping of embedded
device object files. Currently its internals are not able to be tested
easily. This patch adds the `--dry-run` and `--print-wrapped-module`
options to investigate the link jobs that will be run along with the
wrapped code that will be created to register the binaries.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D124039