Throwing a non-copyable exception

[jensmaurer]

clang -std=c++20 accepts the following program:

struct S
{
  S() = default;
  S(const S&) = delete;
};

int main()
{
  try {
    throw S();         // #1
  } catch (S s) {
    return 1;
  }
}

but it is ill-formed at #1 according to [except.throw] p5. (We need to be able to copy exception objects in a type-erased manner for std::exception_ptr on implementations without reference-counted exceptions.)

Cross-reference: gcc bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106812

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[CaseyCarter]

This is a duplicate of #53224.