This patch to configure makes the --tune option recognise k8 core cpus

(athlon64, opteron, etc).  Currently configure just spits a warning,
saying "unknown cpu type", and doesn't set the --march compile flag.
Patch by Chris Halse Rogers <chalserogers at gmail com>.

Originally committed as revision 4627 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -754,7 +754,7 @@ if test $tune != "generic"; then
 	    TUNECPU=ppc970
             POWERPCMODE="64bits"
 	;;
-	i[3456]86|pentium|pentiumpro|pentium-mmx|pentium[234]|prescott|k6|k6-[23]|athlon|athlon-tbird|athlon-4|athlon-[mx]p|winchip-c6|winchip2|c3|nocona)
+	i[3456]86|pentium|pentiumpro|pentium-mmx|pentium[234]|prescott|k6|k6-[23]|athlon|athlon-tbird|athlon-4|athlon-[mx]p|winchip-c6|winchip2|c3|nocona|athlon64|k8|opteron|athlon-fx)
 	    CFLAGS="$CFLAGS -march=$tune"
 	;;
 	*)