[OpenMP] Enable the existing nocudalib flag for OpenMP offloading toolchain.

Summary: Enable the -nocudalib flag for the OpenMP device offloading toolchain as well. Currently it can only be used for the CUDA toolchain.

Reviewers: Hahnfeld, ABataev, carlo.bertolli, caomhin, hfinkel, tra

Reviewed By: tra

Subscribers: hfinkel, cfe-commits

Differential Revision: https://reviews.llvm.org/D37913

llvm-svn: 314164