in6addr_any is defined as extern in IRIX header files, but is not actually

contained in any library (sigh).

Make this check fail, if the link stage does not succeed.  Also avoid
GCC optimization which drops the reference to ip6addr_any.

Tested on IRIX 6.5.15.

configure.in

@@ -467,10 +467,10 @@ fi
 
 dnl Check for IPv6 support
 AC_CACHE_CHECK([for IPv6 support], ac_cv_ipv6_support,
-[AC_TRY_COMPILE([ #include <sys/types.h>
+[AC_TRY_LINK([ #include <sys/types.h>
 #include <sys/socket.h>
-#include <netinet/in.h>], [struct sockaddr_in6 s; struct in6_addr t=in6addr_any; int i=AF_INET6; s],
-  ac_cv_ipv6_support=yes, ac_cv_ipv6_support=no)])
+#include <netinet/in.h>], [struct sockaddr_in6 s; struct in6_addr t=in6addr_any; int i=AF_INET6; s; t.s6_addr[0] = 0;],
+  [ac_cv_ipv6_support=yes], [ac_cv_ipv6_support=no])])
 if test "$ac_cv_ipv6_support" = yes; then
   AC_DEFINE(HAVE_IPV6,1,[Whether you have IPv6 support])
 fi