Add accept4() for NetBSD, Illumos and Solaris

References:
* NetBSD (became available with 8.0):
  http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/sys/socket.h?annotate=1.129&only_with_tag=MAIN
  http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/sys/accept4.c?annotate=1.2&only_with_tag=MAIN
* Illumos:
  https://illumos.org/man/3socket/accept
  https://github.com/illumos/illumos-gate/blob/master/usr/src/uts/common/sys/socket.h
  https://github.com/illumos/illumos-gate/blob/master/usr/src/lib/libsocket/socket/weaks.c
* Solaris:
  https://docs.oracle.com/cd/E88353_01/html/E37843/accept-3c.html

Author: tormol

src/unix/bsd/netbsdlike/mod.rs

@@ -632,6 +632,12 @@ extern "C" {
     ) -> ::c_int;
 
     pub fn daemon(nochdir: ::c_int, noclose: ::c_int) -> ::c_int;
+    pub fn accept4(
+        s: ::c_int,
+        addr: *mut ::sockaddr,
+        addrlen: *mut ::socklen_t,
+        flags: ::c_int,
+    ) -> ::c_int;
     pub fn mincore(
         addr: *mut ::c_void,
         len: ::size_t,

src/unix/bsd/netbsdlike/openbsd/mod.rs

@@ -1393,12 +1393,6 @@ extern "C" {
         tp: *const ::timeval,
         tz: *const ::timezone,
     ) -> ::c_int;
-    pub fn accept4(
-        s: ::c_int,
-        addr: *mut ::sockaddr,
-        addrlen: *mut ::socklen_t,
-        flags: ::c_int,
-    ) -> ::c_int;
     pub fn execvpe(
         file: *const ::c_char,
         argv: *const *const ::c_char,

src/unix/solarish/mod.rs

@@ -2347,6 +2347,12 @@ extern "C" {
         msg: *mut ::msghdr,
         flags: ::c_int,
     ) -> ::ssize_t;
+    pub fn accept4(
+        fd: ::c_int,
+        address: *mut sockaddr,
+        address_len: *mut socklen_t,
+        flags: ::c_int
+    ) -> ::c_int;
 
     pub fn mq_open(name: *const ::c_char, oflag: ::c_int, ...) -> ::mqd_t;
     pub fn mq_close(mqd: ::mqd_t) -> ::c_int;