[ThinLTO] Implement -pass-remarks-output in ThinLTOCodeGenerator

Summary:
This will also be added to the LTO API, right now this will
bring ThinLTO on par with Monolithic LTO on Darwin.

Reviewers: anemet

Subscribers: tejohnson, llvm-commits

Differential Revision: https://reviews.llvm.org/D26886

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287450 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed