to get rid of restrict qualifier discarding. This lets libc compile
cleanly in gnu99 mode.
Suggested by: kib, christoph.mallon at gmx.de
Approved by: kib (mentor)
when the current implementation won't use it, anyway. Just pass NULL.
This will need to be changed when state-dependent encodings are
supported, but there's no need to take the performance hit
in the meantime.