[PM] Make AnalysisManager::registerPass take its parameter by universal reference.

Summary:
Previously, we were forcing a copy if you passed an lvalue argument; now
we'll take it by reference.

Reviewers: chandlerc

Subscribers: mehdi_amini, silvas, llvm-commits

Differential Revision: https://reviews.llvm.org/D27370

llvm-svn: 288594