[clang] [Clang][CodeGen] Track EH cleanup depth for guarded init and pop correctly (PR #199508)

[Akira Hatanaka via cfe-commits]

ahatanak wrote:

> For non-ARC, no matter what order we do the destruction, it still blows up if you call the function more than once: the block itself gets destroyed when the first call returns, and we never run the initialization again. The only way to make it usable would be to do something like C++ lifetime extension to make the block itself have static lifetime (along the lines of how `static const A& a = A();` works).

A few thoughts:

1. This can be fixed if the block is copied via `__Block_copy` and assigned it to `b` after the static initialization. `b` then points to a heap block, so later calls are fine. But the captures have to be kept alive until the block is copied.
2.  Even without the `__Block_copy`, the function is well defined if it only runs once. I don't think anything in the standard makes the code invalid just because it can't be invoked more than once.

https://github.com/llvm/llvm-project/pull/199508