[TargetTransformInfo][NFCI] Add TargetTransformInfo::isZExtFree.

Summary:
This function is not used in this change but will be used in a
subsequent change.

Reviewers: mcrosier, chandlerc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9180

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243347 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed