Meta: Pass -- to sudo instead of '$SHELL -c' in build scripts

fddbd11baa made it so the command executed
read `sh -c -- '"script" args*'`, the -- in this command is redundant as
the script name never starts with a dash and can never be interpreted as
an option or a flag.
The actually meaningful placement for -- here is after `$SUDO`, to make
sure `$SUDO` does not incorrectly treat `-c` as an option to itself, and
`$SHELL` cannot be interpreted as an option/flag in the extremely
unlikely event that it starts with a dash.

Meta/build-image-extlinux.sh

@@ -8,7 +8,7 @@ script_path=$(cd -P -- "$(dirname -- "$0")" && pwd -P)
 
 if [ "$(id -u)" != 0 ]; then
     set +e
-    ${SUDO} "${SHELL}" -c -- "\"$0\" $* || exit 42"
+    ${SUDO} -- "${SHELL}" -c "\"$0\" $* || exit 42"
     case $? in
         1)
             die "this script needs to run as root"