Build failure on macOS Sonoma 14.0 beta

[Hans Åberg]

> On 20 Sep 2023, at 22:45, Marc Culler <marc.culler at gmail.com> wrote:
> 
> I learned by reading the release notes for XCode 15 that Apple rewrote the linker for XCode 15.  They also made the old linker available by using -ld64 as a linker option.

One should use -ld_classic as -ld64 is deprecated by a warning I got from the linker. 

Also, this is an issue for MacPorts gcc12; clang-16 works with new linker.