[ADT] Add CachedHashString.

Summary:
This is like CachedHashStringRef, but owns its data.

This lets us use strings inside of DenseMaps.

Reviewers: timshen

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D25645

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284871 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed