[Verifier] Improve error for cross-module refs

By including the module name in the error message.
This makes the error message much more useful and
saves a trip to the debugger.

Reviewers: dexonsmith

Subscribers: dexonsmith, llvm-commits

Differential Revision: http://reviews.llvm.org/D14473

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254437 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed