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

[via cfe-commits]

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@@ -551,3 +551,14 @@ struct full_of_empty empty_test_2(void) {
   struct full_of_empty e;
   return e; // no-warning
 }
+
+struct with_explicit_field {
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higher-performance wrote:

Done.

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