add pipe2 to non-OSX BSD's

https://github.com/rust-lang/libc/pull/501

src/unix/bsd/freebsdlike/mod.rs

@@ -907,6 +907,7 @@ extern {
                          abstime: *const ::timespec) -> ::c_int;
     pub fn pthread_mutex_timedlock(lock: *mut pthread_mutex_t,
                                    abstime: *const ::timespec) -> ::c_int;
+    pub fn pipe2(fds: *mut ::c_int, flags: ::c_int) -> ::c_int;
 }
 
 cfg_if! {

src/unix/bsd/netbsdlike/mod.rs

@@ -535,6 +535,7 @@ extern {
     pub fn sethostname(name: *const ::c_char, len: ::size_t) -> ::c_int;
     pub fn pthread_mutex_timedlock(lock: *mut pthread_mutex_t,
                                    abstime: *const ::timespec) -> ::c_int;
+    pub fn pipe2(fds: *mut ::c_int, flags: ::c_int) -> ::c_int;
 }
 
 cfg_if! {