[lld] Fix --exclude-libs broken when --whole-archive is used

Summary:
**Problem**
`--exclude-libs` does not work for static libraries affected by the `--whole-archive` option.

**Description**
`--exclude-libs` creates a list of static library paths and does library lookups in this list.
`--whole-archive` splits the static libraries that follow it into separate objects. As a result, lld no longer sees static libraries among linked files and does no `--exclude-libs` lookups.

**Solution**
The proposed solution is to make `--exclude-libs` consider object files too. When lld finds an object file it checks whether this file originates from an archive and, if so, looks the archive up in the `--exclude-libs` list.

Reviewers: ruiu, rafael

Reviewed By: ruiu

Subscribers: asl, ikudrin, llvm-commits, emaste

Tags: #lld

Differential Revision: https://reviews.llvm.org/D39353

llvm-svn: 316998