[clang] [CIR] Upstream `AddressSpace` support for `PointerType` (PR #161028)

[Andy Kaylor via cfe-commits]

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@@ -73,13 +74,17 @@ struct CIRGenTypeCache {
   /// The alignment of size_t.
   unsigned char SizeAlignInBytes;
 
+  LangAS ASTAllocaAddressSpace;
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andykaylor wrote:

```suggestion
  cir::TargetAddressSpaceAttr cirAllocaAddressSpace;
```
We can change the type of this to `mlir::Attribute` when support for two kinds of address space attributes is added, but for now, let's make it specific.

https://github.com/llvm/llvm-project/pull/161028