[Driver][OpenMP][CUDA] Add capability to bundle object files in sections of the host binary format.

Summary:
This patch adds the capability to bundle object files in sections of the host binary using a designated naming convention for these sections. This patch uses the functionality of the object reader already in the LLVM library to read bundled files, and invokes clang with the incremental linking options to create bundle files. 

Bundling files involves creating an IR file with the contents of the bundle assigned as initializers of globals binded to the designated sections. This way the bundling implementation is agnostic of the host object format.

The features added by this patch were requested in the RFC discussion in  http://lists.llvm.org/pipermail/cfe-dev/2016-February/047547.html.

Reviewers: echristo, tra, jlebar, hfinkel, ABataev, Hahnfeld

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

Differential Revision: https://reviews.llvm.org/D21851

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@279634 91177308-0d34-0410-b5e6-96231b3b80d8