llvm-link: Improve diagnostic for module-level metadata mismatch

This might produce hard to read/illegible diagnostics for especially
weird/non-trivial module metadata but integers are about all we are
using these days, so seems more useful than not.

Patch based on work by Kristina Brooks - thanks!

Differential Revision: https://reviews.llvm.org/D52952

llvm-svn: 344011