Disable loop unrolling and icp in SamplePGO ThinLTO compile phase

Summary:
loop unrolling and icp will make the sample profile annotation much harder in the backend. So disable these 2 optimization in the ThinLTO compile phase.
Will add a test in cfe in a separate patch.

Reviewers: tejohnson

Reviewed By: tejohnson

Subscribers: mehdi_amini, llvm-commits, Prazek

Differential Revision: https://reviews.llvm.org/D31217

llvm-svn: 298646