Small patch for NetBSD

[Jim Meyering]

Richard Henderson <rth@cygnus.com> writes:
| > strsignal()?
| >
| > While it's obvious what it's supposed to do, when did that come into play?
| > I can't find it in C89 or C9X...
|
| It is likely a GNU extension.  I find it on Linux libc5 and glibc
| only.  I have no idea when or where it was first introduced, though
| it is such an obvious thing.  We also have psignal(), fwiw.
|
| In any case, it is something to have autoconf check for at the same
| time as sys_errlist and sys_siglist, and, as I described earlier,
| we should preferentially use the functions.

It's in Solaris 5.5.1, too.
There's a strsignal.c in libiberty for those who want to use autoconf's
AC_REPLACE_FUNCS.