CodeGen: alter CFConstantString class name for swift 5.0 Swift 5.0 has changed the name decoration for swift symbols, using a 'S' sigil rather than 's' as in 4.2. Adopt the new convention. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@345291 91177308-0d34-0410-b5e6-96231b3b80d8