Call TargetMachine::addEarlyAsPossiblePasses from BackendUtil.
Call TargetMachine::addEarlyAsPossiblePasses from BackendUtil.

Summary:
As of D18614, TargetMachine exposes a hook to add a set of passes that should
be run as early as possible.  Invoke this hook from clang when setting up the
pass manager.

Reviewers: chandlerc

Subscribers: rnk, cfe-commits, tra

Differential Revision: http://reviews.llvm.org/D18617

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@267764 91177308-0d34-0410-b5e6-96231b3b80d8

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