Add missing std::move in Replacements::add

This diff adds std::move to avoid copying of 
the Replacement NewR in the method Replacements::add.

Test plan: make -j8 check-all

Differential revision: https://reviews.llvm.org/D25049


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@282949 91177308-0d34-0410-b5e6-96231b3b80d8