Improve LinkModules warnings

Provide triple and data layout as well as module names (or empty string) when there's a mismatch.

Differential Revision: http://llvm-reviews.chandlerc.com/D2971

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203009 91177308-0d34-0410-b5e6-96231b3b80d8