[Clang][OpenMP] Add partial support for Static Device Libraries

An archive containing device code object files can be passed to
clang command line for linking. For each given offload target
it creates a device specific archives which is either passed to llvm-link
if the target is amdgpu, or to clang-nvlink-wrapper if the target is
nvptx. -L/-l flags are used to specify these fat archives on the command
line. E.g.
  clang++ -fopenmp -fopenmp-targets=nvptx64 main.cpp -L. -lmylib

It currently doesn't support linking an archive directly, like:
  clang++ -fopenmp -fopenmp-targets=nvptx64 main.cpp libmylib.a

Linking with x86 offload also does not work.

Reviewed By: ye-luo

Differential Revision: https://reviews.llvm.org/D105191