Add hashing and DenseMapInfo for ArrayRef

Sometimes it is more natural to use a ArrayRef<uint8_t> than a StringRef to
represent a range of bytes that is not, semantically, a string.

This will be used in lld in a sec.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250658 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed