Add StringRef::take_front and StringRef::take_back

Reviewed By: majnemer, rnk
Differential Revision: https://reviews.llvm.org/D23965

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280114 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed