[ThinLTO] Support opt remarks options with distributed ThinLTO backends

Summary:
Passes down the necessary code ge options to the LTO Config to enable
-fdiagnostics-show-hotness and -fsave-optimization-record in the ThinLTO
backend for a distributed build.

Also, remove warning about not having PGO when the input is IR.

Reviewers: pcc

Subscribers: mehdi_amini, inglorion, eraman, cfe-commits

Differential Revision: https://reviews.llvm.org/D46464

llvm-svn: 331592