[Driver][OpenMP] Add logic for offloading-specific argument translation.

Summary:
This patch includes support for argument translation that is specific of a given offloading kind. Additionally, it implements the translation for OpenMP device kinds in the gcc tool chain.

With this patch, it is possible to compile a functional OpenMP application with offloading capabilities with no separate compilation.

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

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

Differential Revision: https://reviews.llvm.org/D21848

llvm-svn: 285320