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

[Erich Keane via cfe-commits]

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@@ -4505,6 +4505,14 @@ bool FieldDecl::isZeroSize(const ASTContext &Ctx) const {
   if (!CXXRD->isEmpty())
     return false;
 
+  // MS ABI: nonzero if class type with class type fields
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erichkeane wrote:

Does any differentiation need to be made between the spellings on 4489?  Additionally, can you elaborate on the comment here?  How can we look at the fields of `CXXRD` if it is empty?  

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