[clang] [clang][constexpr] Move anonymous-union check before getDestructor() in HandleDestructionImpl (PR #197416)

[A. Jiang via cfe-commits]

frederick-vs-ja wrote:

Thanks! You can link your pull request to this issue using [GitHub's close/fix/resolve syntax](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword).
(in the PR description not the commit message)

https://github.com/llvm/llvm-project/pull/197416