When `llvm.global_ctors` has no elements (e.g., when all resources are
unused in a shader library), its initializer is a `zeroinitializer`
(`ConstantAggregateZero`) rather than a `ConstantArray`. The previous
code used `cast<ConstantArray>` which asserts on incompatible types:
> "cast<Ty>() argument of incompatible type!"
This patch uses `dyn_cast` and returns early if the initializer is not a
`ConstantArray`, handling the edge case gracefully.
Fixes#178993.
Co-authored-by: Kaitlin Peng <kaitlinpeng@microsoft.com>
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