[clang] [clang][Sema] Fix crash on atomic builtins with incomplete type args (PR #96374)

[Aaron Ballman via cfe-commits]

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@@ -4570,7 +4570,8 @@ ExprResult Sema::BuildAtomicExpr(SourceRange CallRange, SourceRange ExprRange,
   }
 
   // Pointer to object of size zero is not allowed.
-  if (Context.getTypeInfoInChars(AtomTy).Width.isZero()) {
+  if (!AtomTy->isIncompleteType() &&
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AaronBallman wrote:

If you call `RequireCompleteType()` before this `if` instead of checking for an incomplete type, do you get better diagnostic behavior?

https://github.com/llvm/llvm-project/pull/96374