This patch makes "&Cls::purevfn" not an odr use. This isn't what the standard

This patch makes "&Cls::purevfn" not an odr use. This isn't what the standard
says, but that's a defect (to be filed). "Cls::purevfn()" is still an odr use.

Also fixes a bug that caused us to not mark the function referenced just
because we didn't want to mark it odr used.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174242 91177308-0d34-0410-b5e6-96231b3b80d8