if unknown configure options are passed, ffmpeg exits. this patch skips
unknown args

Index: ffmpeg-3.4/configure
===================================================================
--- ffmpeg-3.4.orig/configure
+++ ffmpeg-3.4/configure
@@ -3607,7 +3607,7 @@ for opt do
         ;;
         --enable-*=*|--disable-*=*)
             eval $(echo "${opt%%=*}" | sed 's/--/action=/;s/-/ thing=/')
-            is_in "${thing}s" $COMPONENT_LIST || die_unknown "$opt"
+            is_in "${thing}s" $COMPONENT_LIST || continue
             eval list=\$$(toupper $thing)_LIST
             name=$(echo "${optval}" | sed "s/,/_${thing}|/g")_${thing}
             list=$(filter "$name" $list)
@@ -3632,12 +3632,12 @@ for opt do
             elif is_in $option $CMDLINE_SELECT; then
                 $action $option
             else
-                die_unknown $opt
+                continue
             fi
         ;;
         --list-*)
             NAME="${opt#--list-}"
-            is_in $NAME $COMPONENT_LIST || die_unknown $opt
+            is_in $NAME $COMPONENT_LIST || continue
             NAME=${NAME%s}
             eval show_list $NAME \$$(toupper $NAME)_LIST
         ;;
@@ -3659,7 +3659,7 @@ for opt do
             elif is_in $optname $CMDLINE_APPEND; then
                 append $optname "$optval"
             else
-                die_unknown $opt
+                continue
             fi
         ;;
     esac