This is similar to Metadata.def and Instructions.def but for Value's.
It will be used in upcoming commits to devirtualize the Value class.
Reviewed by Duncan Exon Smith.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240358 91177308-0d34-0410-b5e6-96231b3b80d8
