[ThinLTO] Ensure sanitizer passes are run

Summary:
In ThinLTO compilation, we exit populateModulePassManager early and
were not adding PM extension passes meant to run at the end of the
pipeline. This includes sanitizer passes. Add these passes before
the early exit.

A test will be added to projects/compiler-rt.

Reviewers: pcc

Subscribers: mehdi_amini, inglorion, llvm-commits

Differential Revision: https://reviews.llvm.org/D39565

llvm-svn: 317714