Build failure on macOS Sonoma 14.0 beta

[Hans Åberg]

> On 20 Sep 2023, at 16:36, Marc Culler <marc.culler at gmail.com> wrote:
> 
> …macOS Sonoma beta…
…
> …using: "Apple clang version 15.0.0
> (clang-1500.0.40.1)"

The same compiler version is now available on MacOS 13, together with Xcode 15.