Dump what value failed byval attribute verification

This verifier check is failing for us while doing ThinLTO on Chrome for
x86, see https://crbug.com/978218, and this helps to debug the problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364357 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed