[clang] [Clang] suppress deprecated field warnings in implicit special-member functions (PR #147400)

[Shashi Shankar via cfe-commits]

================
@@ -547,6 +547,15 @@ static void DoEmitAvailabilityWarning(Sema &S, AvailabilityResult K,
     return;
   }
   case AR_Deprecated:
+    // Suppress -Wdeprecated-declarations in purely implicit special-member functions.
+    if (auto *MD = dyn_cast_if_present<CXXMethodDecl>(S.getCurFunctionDecl());
+        MD && MD->isImplicit() && MD->isDefaulted() &&
+        (isa<CXXConstructorDecl, CXXDestructorDecl>(MD) ||
+        MD->isCopyAssignmentOperator() ||
+        MD->isMoveAssignmentOperator())) {
+    return;
+    }
+
----------------
shashforge wrote:

@zwuis  – just to clarify:

* @cor3ntin  review comment has already been addressed**: the early-exit now lives in Sema::ShouldWarnAboutDeprecatedDecl`, exactly as suggested.
* This was pushed **before** I re-requested review.
* Relevant code, now on `HEAD`:

```cpp
    if (const auto *FD = dyn_cast_or_null<FunctionDecl>(S.getCurFunctionDecl());
        FD && FD->isImplicit())
      return;
}
```
 `ninja check-clang` is green.

Let me know if I missed anything—happy to tweak further!

https://github.com/llvm/llvm-project/pull/147400