[clang] [Clang][LLVM][Coroutines] Prevent __coro_gro from outliving __promise (PR #66706)

[Wei Wang via cfe-commits]

apolloww wrote:

Thanks for the fix! I think originally the deferred conversion is placed after `coro.end` so that it won't be counted as "use across suspend point", but it doesn't stop optimizer from breaking that assumption. 

https://github.com/llvm/llvm-project/pull/66706