[clang] Add Clang attribute to ensure that fields are initialized explicitly (PR #102040)

[Erich Keane via cfe-commits]

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@@ -81,6 +82,7 @@ CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
       HasPrivateFields(false), HasProtectedFields(false),
       HasPublicFields(false), HasMutableFields(false), HasVariantMembers(false),
       HasOnlyCMembers(true), HasInitMethod(false), HasInClassInitializer(false),
+      HasUninitializedExplicitInitFields(false),
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erichkeane wrote:

THIS I think makes sense as the alternative cost is too high, despite having a cost on every `CXXRecordDecl`.

That said, should this be on `RecordDecl` instead?

https://github.com/llvm/llvm-project/pull/102040