[PGO] Clang part of change for context-sensitive PGO (part1)

Part 1 of CSPGO change in Clang. This includes changes in clang options
and calls to llvm PassManager. Tests will be committed in part2.
This change needs the PassManager change in llvm.

Differential Revision: https://reviews.llvm.org/D54176

llvm-svn: 355331