[clang] [llvm] [TableGen] Change SetTheory set/vec to use const Record * (PR #107692)

[Rahul Joshi via cfe-commits]

jurahul wrote:

> lgtm assuming the const_cast goes away in a subsequent change

Thanks. Yeah as I said above, I think we can make the Record* in DefInit const and then get rid of the const_cast<>. But the mutable for CorrespondingDefInit  will stay, with it serving as a cache.

https://github.com/llvm/llvm-project/pull/107692