[ThinLTO] Rename variables used in metadata linking (NFC)

As suggested in review for r255909, rename MDMaterialized to AllowTemps,
and identify the name of the boolean flag being set in calls to
saveMetadataList.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256653 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed