[OpenMP] Add support for linking AMDGPU images

This patch adds support for linking AMDGPU images using the LLD binary.
AMDGPU files are always bitcode images and will always use the LTO
backend. Additionally we now pass the default architecture found with
the `amdgpu-arch` tool to the argument list.

Depends on D117156

Differential Revision: https://reviews.llvm.org/D117246