[clang] Reapply "[Clang][CWG1815] Support lifetime extension of temporary created by aggregate initialization using a default member initializer" (PR #108039)

[Erich Keane via cfe-commits]

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@@ -7810,9 +7813,11 @@ class Sema final : public SemaBase {
   }
 
   bool isInLifetimeExtendingContext() const {
-    assert(!ExprEvalContexts.empty() &&
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erichkeane wrote:

Sure, but why would this be in a case where we're not in an evaluation context?  You're removing the assert, and it doesn't seem to make sense to check a context when we don't have one.

https://github.com/llvm/llvm-project/pull/108039