Use llvm::utohexstr instead of Twine::utohexstr.
Use llvm::utohexstr instead of Twine::utohexstr.

They are essentially the same in this context, so I prefer the one
that doesn't need `Twine::`.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@287814 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld