[LinkerWrapper] Fix static library symbol resolution

The linker wrapper performs its own very basic symbol resolution for the
purpose of supporting standard static library semantics. We do this here
because the Nvidia `nvlink` wrapper does not support static linking and
we have some offloading specific extensions.

Currently, we always place symbols in the "table" even if they aren't
extracted. This caused the logic to fail when many files were used that
referenced the same undefined variable. This patch changes the pass to
only add the symbols to the global "table" if the file is actually
extracted.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D151839