[clang] [CIR] Upstream the initial BlockAddressOp implementation (PR #168151)

[Henrich Lauko via cfe-commits]

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@@ -0,0 +1,21 @@
+// RUN: cir-opt %s -verify-diagnostics -split-input-file --verify-roundtrip
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xlauko wrote:

nit: sorry no roundgtrip here, as there is nothing to roundtrip since we error out on parsing.

```suggestion
// RUN: cir-opt %s -verify-diagnostics -split-input-file
```

https://github.com/llvm/llvm-project/pull/168151