PATCH: silence warning in libiberty/pex-unix.c

[Ben Elliston]

> > -#define writeerr(s) write (STDERR_FILE_NO, s, strlen (s))
> > +#define writeerr(s) if (write (STDERR_FILE_NO, s, 0) < 0) _exit (-1)
> 
> Just cast the result to (void).  I'll preapprove that patch if that
> works.

Casting function results to (void) is insufficient to eliminate the
warning.  Whether or not that is a bug is debatable, but I certainly
expected it to work when I first tried it.

Ben