CodeGen: Mark the runtime function __dynamic_cast as readonly & nounwind.

This allows the optimizer to CSE dynamic_casts.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174289 91177308-0d34-0410-b5e6-96231b3b80d8
Comment to XML conversion: replace string comparison with command ID comparison


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174290 91177308-0d34-0410-b5e6-96231b3b80d8