[PartialInlining] Add internal options to enable partial inlining in pass pipeline (off by default)

1. Legacy: -mllvm -enable-partial-inlining
2. New:  -mllvm -enable-npm-partial-inlining -fexperimental-new-pass-manager

Differential Revision: http://reviews.llvm.org/D33382

llvm-svn: 303567