message: Fix automatic description for AnyTypeOf
  Unfortunately, this now gives a segfault if you pass it an empty list, similar to stringify. Given how fiddly this is, we should probably have a string join helper. I'll fix both of these using better tablegen helpers in a follow-up.
diff: @@ -271,7 +271,7 @@ class AnyTypeOf<list<Type> allowedTypes, string description = ""> : Type<
  !if(!eq(description, ""),
  // Join all allowed types' descriptions with " or " as the description
  // if not provided during template specialization
  - !foldl(/*init*/"", /*list*/allowedTypes, prev, cur,
  + !foldl(!head(allowedTypes).description, !tail(allowedTypes), prev, cur,
  prev # " or " # cur.description),
  // Otherwise use the provided one
  description)>;
  