Verifier: Update assert message to reflect LangRef

No functionality change, just correcting the assertion message.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211977 91177308-0d34-0410-b5e6-96231b3b80d8
Fix build following r211956

RuntimeDyld now uses MCInst::dump_pretty() which introduces a dependency on
'MC'.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211978 91177308-0d34-0410-b5e6-96231b3b80d8