[flang] [llvm] [mlir] [Flang]Fix for changed code at the end of AllocaIP. (PR #92430)

[Mats Petersson via llvm-commits]

Leporacanthicus wrote:

@Meinersbur The case is not that we are using `alloca` in conditionals - but that we do something like `if thing.is_allocated() then allocate-and copy into private variable`  - we do the `alloca`, unconditionally. But those `if allocated` means there's an alternative path, so there's new blocks being created. And this means the end marker used in the original block gets changed so any previously stored insertion point becomes invalid.

I'm still trying to make this work correctly for all cases.

https://github.com/llvm/llvm-project/pull/92430