Ref T12855. Throwable does not exist in PHP5, but can be used safely in this construct, at a minimum:
} catch (Exception $ex) {
} catch (Throwable $ex) {We could heavily overachive here by trying to make sure that uses of Throwable were all safe, but I suspect we'll end up with about 15 uses and never really have problems with this. Until this is a real problem, just stop the analyzer from complaining about Throwable and Error.