Add sample PGO support to ThinLTO new pass manager.

Summary:
For SamplePGO + ThinLTO, because profile annotation is done twice at both PrepareForThinLTO pipeline and backend compiler, the following changes are needed at the PrepareForThinLTO phase to ensure the IR is not changed dramatically. Otherwise the profile annotation will be inaccurate in the backend compiler.

* disable hot-caller heuristic
* disable loop unrolling
* disable indirect call promotion

This will unblock the new PM testing for sample PGO (tools/clang/test/CodeGen/pgo-sample-thinlto-summary.c), which will be covered in another cfe patch.

Reviewers: chandlerc, tejohnson, davidxl

Reviewed By: tejohnson

Subscribers: sanjoy, mehdi_amini, Prazek, inglorion, llvm-commits

Differential Revision: https://reviews.llvm.org/D34895

llvm-svn: 307437