Add order-dependencies to object libraries

Summary: If you are generating an object library that depends on table-gen generate sources, you need the object library to depend on the tablgen target. Currently llvm_add_library doesn't add dependencies for object libraries at all, which is clearly problematic.

Reviewers: compnerd, hintonda, smeenai

Reviewed By: smeenai

Subscribers: mgorny, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65818

llvm-svn: 368074