[clang] Implement [[msvc::no_unique_address]] (PR #65675)

[Erich Keane via cfe-commits]

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@@ -1798,11 +1798,13 @@ def ArmMveStrictPolymorphism : TypeAttr, TargetSpecificAttr<TargetARM> {
   let Documentation = [ArmMveStrictPolymorphismDocs];
 }
 
-def NoUniqueAddress : InheritableAttr, TargetSpecificAttr<TargetItaniumCXXABI> {
-  let Spellings = [CXX11<"", "no_unique_address", 201803>];
+def NoUniqueAddress : InheritableAttr {
+  let Spellings = [CXX11<"", "no_unique_address", 201803>,
+                   CXX11<"msvc", "no_unique_address", 201803>];
+  let Accessors = [Accessor<"isDefault", [CXX11<"", "no_unique_address", 201803>]>,
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erichkeane wrote:

```suggestion
  let Accessors = [Accessor<"isStandard", [CXX11<"", "no_unique_address", 201803>]>,
```

https://github.com/llvm/llvm-project/pull/65675