configure: fix filter() function when matching multiple patterns

This makes comma-separated patters to --disable-decoder and friends
work correctly with POSIX-compliant shells.

Originally committed as revision 19688 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -295,7 +295,7 @@ filter(){
     pat=$1
     shift
     for v; do
-        case "$v" in $pat) echo "$v" ;; esac
+        eval "case $v in $pat) echo $v ;; esac"
     done
 }