configure.ac: add IA64 support.

ia64 on Linux can use DRI as well.

Reported-by: russiane39 on #radeon
Bugzilla: http://bugs.freedesktop.org/show_bug.cgi?id=48788
Signed-off-by: Dave Airlie <airlied@redhat.com>

configure.ac

@@ -708,7 +708,7 @@ default_driver="xlib"
 case "$host_os" in
 linux*)
     case "$host_cpu" in
-    i*86|x86_64|powerpc*|sparc*) default_driver="dri";;
+    i*86|x86_64|powerpc*|sparc*|ia64*) default_driver="dri";;
     esac
     ;;
 *freebsd* | dragonfly* | *netbsd*)