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SCO (formarly Caldera) has 3 OS product lines.
UnixWare (which includes OpenUNIX)
Open Server 5
and OpenLinux.
The patch primarly address the Open Server 5 product.
Here is a table of $ac_sys_system (uname -s) values.
UnixWare 2.03   UNIX_SV
UnixWare 2.1.3  UNIX_SV
UnixWare 7.1.1  UnixWare
OpenUnix 8.0.0  OpenUNIX
Open Server 5   SCO_SV

So no, 
+       case $ac_sys_system in
+           SCO_SV*) OPT="$OPT -m486 -DSCO5";;
+       esac
will not interfere with UnixWare.

The -KPIC for UnixWare is correct but for 
Open Server, the option is -Kpic

In HEAD, 
#if defined(__USLC__) && defined(__SCO_VERSION__
#define STRICT_SYSV_CURSES /* Don't use ncurses extensions
*/
#endif
should really be replaced with a configure 
time test.  HEAD still needs a lot of work
for UnixWare and Open Server. Perhaps i'll
have time in november.