[Driver][OpenMP] Update actions builder to create bundling action when necessary.

Summary:
In order to save the user from dealing with multiple output files (for host and device) while using separate compilation, a new action `OffloadBundlingAction` is used when the last phase is not linking. This action will then result in a job that uses the proposed bundling tool to create a single preprocessed/IR/ASM/Object file from multiple ones.

The job creation for the new action will be proposed in a separate patch.

Reviewers: echristo, tra, jlebar, ABataev, hfinkel

Subscribers: whchung, mehdi_amini, cfe-commits, Hahnfeld, andreybokhanko, arpith-jacob, carlo.bertolli, caomhin

Differential Revision: https://reviews.llvm.org/D21852

llvm-svn: 285323