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

But I wonder why nobody stumbled upon this.

I just made a new clone of tz.

I work normally on RHEL 7 (redhat enterprise Linux)
with gcc version 4.8.5 20150623 (Red Hat 4.8.5-44) (GCC)

When I say make or make all, I get something I never observed before:

cc -DTZDIR='"/usr/share/zoneinfo"'    -c -o zic.o zic.c
In file included from zic.c:16:0:
private.h:791:60: error: conflicting types for ‘restrict’
 struct tm *localtime_rz(timezone_t restrict, time_t const *restrict,
                                                            ^
private.h:791:36: note: previous definition of ‘restrict’ was here
 struct tm *localtime_rz(timezone_t restrict, time_t const *restrict,
                                    ^
private.h:792:15: error: conflicting types for ‘restrict’
    struct tm *restrict);
               ^
private.h:791:60: note: previous definition of ‘restrict’ was here
 struct tm *localtime_rz(timezone_t restrict, time_t const *restrict,
                                                            ^
private.h:793:49: error: conflicting types for ‘restrict’
 time_t mktime_z(timezone_t restrict, struct tm *restrict);
                                                 ^
private.h:793:28: note: previous definition of ‘restrict’ was here
 time_t mktime_z(timezone_t restrict, struct tm *restrict);

This does not happen when I compile on RHEL 9
gcc version 11.4.1 20230605 (Red Hat 11.4.1-2) (GCC)

Can anyone point me to a fix?