Revert "Revert "DI: LLVM schema change: fold constants into string"" This reverts commit r218917, effectively reapplying r218913. Original commit message follows. -- Update debug info testcases for an LLVM metadata schema change to fold metadata constant operands into a single `MDString`. Part of PR17891. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219011 91177308-0d34-0410-b5e6-96231b3b80d8