Here's a diff that fixes the problems that folks (including me) where
having when they tried to use newly compiled Dec 15 libraries.
 IMHO function calls in libc/gen/err.c to __vwarn(), __verrx() and __vwarn()
should be changed into _vwarn(), _verrx and _vwarn.
 LAST MINUTE NEWSFLASH: this is the fix the Paul Kranenburg thought of
in a message I saw a couple of seconds ago.

Onno van der Linden     c/o     vdlinden@fwi.uva.nl (Frank van der Linden)
*** /usr/src/lib/libc/gen/_sys_errlist.c.orig	Thu Dec 15 16:42:10 1994
--- /usr/src/lib/libc/gen/_sys_errlist.c	Sat Dec 17 18:07:29 1994
***************
*** 6,8 ****
--- 6,9 ----
  #include <sys/cdefs.h>
  
+ __weak_reference(_sys_errlist, __sys_errlist);
  __weak_reference(_sys_errlist, sys_errlist);
*** /usr/src/lib/libc/gen/_sys_nerr.c.orig	Thu Dec 15 16:42:11 1994
--- /usr/src/lib/libc/gen/_sys_nerr.c	Sat Dec 17 18:07:37 1994
***************
*** 6,8 ****
--- 6,9 ----
  #include <sys/cdefs.h>
  
+ __weak_reference(_sys_nerr, __sys_nerr);
  __weak_reference(_sys_nerr, sys_nerr);
*** /usr/src/lib/libc/gen/_sys_siglist.c.orig	Thu Dec 15 16:42:12 1994
--- /usr/src/lib/libc/gen/_sys_siglist.c	Sat Dec 17 18:07:49 1994
***************
*** 6,8 ****
  #include <sys/cdefs.h>
  
! __weak_reference(__sys_siglist, sys_siglist);
--- 6,9 ----
  #include <sys/cdefs.h>
  
! __weak_reference(_sys_siglist, __sys_siglist);
! __weak_reference(_sys_siglist, sys_siglist);
*** /usr/src/lib/libc/gen/_verr.c.orig	Sat Dec 17 16:13:21 1994
--- /usr/src/lib/libc/gen/_verr.c	Sat Dec 17 18:07:57 1994
***************
*** 6,8 ****
  #include <sys/cdefs.h>
  
! __weak_reference(__verr, verr);
--- 6,9 ----
  #include <sys/cdefs.h>
  
! __weak_reference(_verr, __verr);
! __weak_reference(_verr, verr);
*** /usr/src/lib/libc/gen/_verrx.c.orig	Thu Dec 15 16:42:15 1994
--- /usr/src/lib/libc/gen/_verrx.c	Sat Dec 17 18:08:03 1994
***************
*** 6,8 ****
--- 6,9 ----
  #include <sys/cdefs.h>
  
+ __weak_reference(_verrx, __verrx);
  __weak_reference(_verrx, verrx);
*** /usr/src/lib/libc/gen/_vwarn.c.orig	Thu Dec 15 16:42:15 1994
--- /usr/src/lib/libc/gen/_vwarn.c	Sat Dec 17 18:08:11 1994
***************
*** 6,8 ****
--- 6,9 ----
  #include <sys/cdefs.h>
  
+ __weak_reference(_vwarn, __vwarn);
  __weak_reference(_vwarn, vwarn);
*** /usr/src/lib/libc/gen/_vwarnx.c.orig	Thu Dec 15 16:42:17 1994
--- /usr/src/lib/libc/gen/_vwarnx.c	Sat Dec 17 18:08:28 1994
***************
*** 6,8 ****
--- 6,9 ----
  #include <sys/cdefs.h>
  
+ __weak_reference(_vwarnx, __vwarnx);
  __weak_reference(_vwarnx, vwarnx);
*** /usr/src/lib/libc/gen/_warn.c.orig	Thu Dec 15 16:42:17 1994
--- /usr/src/lib/libc/gen/_warn.c	Sat Dec 17 18:08:51 1994
***************
*** 6,8 ****
--- 6,9 ----
  #include <sys/cdefs.h>
  
+ __weak_reference(_warn, __warn);
  __weak_reference(_warn, warn);
*** /usr/src/lib/libc/gen/_warnx.c.orig	Thu Dec 15 16:42:20 1994
--- /usr/src/lib/libc/gen/_warnx.c	Sat Dec 17 18:08:59 1994
***************
*** 6,8 ****
--- 6,9 ----
  #include <sys/cdefs.h>
  
+ __weak_reference(_warnx, __warnx);
  __weak_reference(_warnx, warnx);