configure: fix cpu=generic case

Originally committed as revision 21300 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1815,7 +1815,9 @@ is_in $arch $ARCH_LIST || echo "WARNING: unknown arch $arch"
 enable $arch
 
 # Add processor-specific flags
-if enabled ppc; then
+if test "$cpu" = generic; then
+    : do nothing
+elif enabled ppc; then
 
     case $cpu in
         601|ppc601|PowerPC601)
@@ -1923,12 +1925,6 @@ elif enabled avr32; then
         ;;
     esac
 
-else
-
-    if test "$cpu" != generic; then
-        echo "WARNING: Unknown CPU \"$cpu\", ignored."
-    fi
-
 fi
 
 add_cflags $cpuflags