flex code modernization: Replace YY_EXTRA_TYPE define with flex option
Replace #define YY_EXTRA_TYPE with %option extra-type. The latter is
the way recommended by the flex manual (available since flex 2.5.34).
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://www.postgresql.org/message-id/flat/
eb6faeac-2a8a-4b69-9189-
c33c520e5b7b@eisentraut.org