[clang] [Clang][counted_by] Support casting the array to a different type (PR #136239)

[Bill Wendling via cfe-commits]

bwendling wrote:

Also, I'm going to have a larger patch coming after this which will support __bdos on pointers with __counted_by. It contains some refactoring which will help readability a bit more.

https://github.com/llvm/llvm-project/pull/136239