Further testing showed that recent patch's use of compound literals also
runs afoul of GCC in unusual configurations, and it appears that C23
requires that it use 'constexpr' sometimes but not others. So let's drop
that and go to the simpler approach that NetBSD uses. This should also
work even with no-longer-supported Microsoft compilers. Proposed further
patch installed and attached.

I hope this is the last thing we need to change before the 2025a release.