adding pthread_sigqueue to haiku.

(backport <#3697>)
(cherry picked from commit cbaa0d8)

Author: devnexen

src/unix/haiku/mod.rs

@@ -1791,6 +1791,7 @@ extern "C" {
         lock: *mut pthread_mutex_t,
         abstime: *const ::timespec,
     ) -> ::c_int;
+    pub fn pthread_sigqueue(thread: ::pthread_t, sig: ::c_int, value: ::sigval) -> ::c_int;
     pub fn pthread_spin_init(lock: *mut ::pthread_spinlock_t, pshared: ::c_int) -> ::c_int;
     pub fn pthread_spin_destroy(lock: *mut ::pthread_spinlock_t) -> ::c_int;
     pub fn pthread_spin_lock(lock: *mut ::pthread_spinlock_t) -> ::c_int;