also use this, and they shouldn't have to have their own prototypes.
- Silence warnings about constness and signedness in ttymsg(). This
includes changing the return value to a `const char *', and changing
the types of `left' and `wret' (both byte counts) to ssize_t.
Reviewed by: bde
Change it to F_SETFD with an arg of 0 to clear O_NONBLOCK.
PR: bin/8681
Submitted by: koyama takahiro <tah@d1.dion.ne.jp>
Prompted by: Nathan Ahlstrom <nrahlstr@winternet.com>