For more context, see
https://github.com/llvm/llvm-project/pull/119269#issuecomment-3075444493,
but briefly, when removing ARCMigrate, I also removed some symbols in
libclang, which constitutes an ABI break that we don’t want, so this pr
reintroduces the removed symbols; the declarations are marked as
deprecated for future removal, and the implementations print an error
and do nothing, which is what we used to do when ARCMigrate was
disabled.
(cherry picked from commit 1600450f9098e5c9cb26840bd53f1be8a2559b7d)
6ee4eedc2a