ficl: instead of pad, emit can use local variable

Pad in forth is used as "scratchpad" and internal implementations
should not use it. Ficl does not really follow this rule and this can fire back.
emit has no need to use pad, we can use local variable instead.

(cherry picked from commit dba7640e44c5ec148a84b0d58c6c9a3c9e5147f3)