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

[via cfe-commits]

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@@ -55,7 +55,7 @@ CXX11(unlikely)
 // CHECK: likely: 201803L
 // CHECK: maybe_unused: 201603L
 // ITANIUM: no_unique_address: 201803L
-// WINDOWS: no_unique_address: 0
+// WINDOWS: no_unique_address: 201803L 
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cor3ntin wrote:

don't we expect `__has_cpp_attribute(no_unique_address)` to be 0 on windows and `__has_cpp_attribute(msvc::no_unique_address)` to be... some value?

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