[ThinLTO] Support cloning of temporary DILocation metadata

This is needed to support linking of module-level metadata as a
postpass after function importing, where we will be leaving temporary
metadata on imported instructions until the postpass metadata import.

Also added unittest. Split from D14838.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254914 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed