[tz] make error

[Guy Harris]

> On Nov 16, 2023, at 11:58 AM, Alois Treindl via tz <tz at iana.org> wrote:

> I fixed it by adding after private.h line 558:
> It now reads
> #if (__STDC_VERSION__ < 199901 && !defined restrict \
>      && (PORT_TO_C89 || defined _MSC_VER))
> # define restrict
> #else
> # define restrict
> #endif

That's equivalent to

	# define restrict

so presumably that's a workaround, rather than a fix.