[clang] Fix null-deref thanks to an attribute on a global declarator chunk (PR #83611)

[Erich Keane via cfe-commits]

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@@ -100,6 +100,12 @@ void AttributePool::takePool(AttributePool &pool) {
   pool.Attrs.clear();
 }
 
+void AttributePool::takeFrom(ParsedAttributesView &List, AttributePool &Pool) {
+  assert(&Pool != this && "AttributePool can't take attributes from itself");
+  llvm::for_each(List.AttrList, [&Pool](ParsedAttr *A) { Pool.remove(A); });
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erichkeane wrote:

You mean reverse the order of the remove/add?  Based on `takeAllFrom` and `takeOneFrom` (https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Sema/ParsedAttr.h#L953), we are consistently inconsistent :)

In this case, I was working from `takeOneFrom` so I ended up in this order, but if there is a good reason to prefer one over the other, I can switch.

https://github.com/llvm/llvm-project/pull/83611