llvm-link: Add support for archive files as inputs

This patch adds support for archive files as inputs to llvm-link. One
of the use-cases is for OpenMP, where device specific libraries need
to be extracted from libraries containing bundled object files. The
clang-offload-bundler will support extracting these archives, which
will be passed into llvm-link, see https://reviews.llvm.org/D80816.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D81109