kk@poe ~/php3 $ make
gcc -g -O2 -O2   -I. -I.          -I/opt/GNUmysql/include/mysql
         -c functions/datetime.c -o functions/datetime.o
functions/datetime.c: In function `_php3_date':
functions/datetime.c:490: structure has no member named `tm_zone'

kk@poe ~/php3 $ uname -a
SunOS poe 5.5.1 Generic_103640-23 sun4m sparc

struct tm is defined as

struct  tm {    /* see ctime(3) */
        int     tm_sec;
        int     tm_min;
        int     tm_hour;
        int     tm_mday;
        int     tm_mon;
        int     tm_year;
        int     tm_wday;
        int     tm_yday;
        int     tm_isdst;
};

on 2.5.1, 2.6. and 2.7.