[Driver][OpenMP] Add support to create jobs for unbundling actions.
Summary:
This patch adds the support to create jobs for the `OffloadBundlingAction` which will invoke the `clang-offload-bundler` tool to unbundle input files.
Unlike other actions, unbundling actions have multiple outputs. Therefore, this patch adds the required changes to have a variant of `Tool::ConstructJob` with multiple outputs.
The way the naming of the results is implemented is also slightly modified so that the same action can use a different offloading prefix for each use by the different offloading actions.
With this patch, it is possible to compile a functional OpenMP binary with offloading support, even with separate compilation.
Reviewers: echristo, tra, jlebar, ABataev, hfinkel
Subscribers: mkuron, whchung, mehdi_amini, cfe-commits, Hahnfeld, andreybokhanko, arpith-jacob, carlo.bertolli, caomhin
Differential Revision: https://reviews.llvm.org/D21857
llvm-svn: 285326