[OpenMP] Use loaded offloading toolchains to add libraries (#87108)

Summary:
We want to pass these GPU libraries by default if a certain offloading
toolchain is loaded for OpenMP. Previously I parsed this from the
arguments because it's only available in the compilation. This doesn't
really work for `native` and it's extra effort, so this patch just
passes in the `Compilation` as an extr argument and uses that. Tests
should be unaffected.