Fix process not waking up on signals on OpenBSD

When using UBF_TIMER_PTHREAD (the UBF handler on OpenBSD), the
timer_pthread_fn function will not signal the main thread with
SIGVTALRM in cases where timer_pthread is armed before
consume_communication_pipe is called.  This is because
consume_communication_pipe will unarm the timer.

Fix this by checking the return value of consume_communication_pipe.
If it returns TRUE and the timer_pthread is disarmed, then signal
the main thread with SIGVTALRM.

On OpenBSD, this fixes TestThread#test_thread_timer_and_interrupt, and
fixes hangs in TestProcess#test_execopts_redirect_open_fifo_interrupt_raise
and TestProcess#test_execopts_redirect_open_fifo_interrupt_print.
It also fixes the use of Ctrl+C/SIGINT in irb on OpenBSD. It does not
cause any test failures on Linux when UBF_TIMER_PTHREAD is forced as
the UBF handler.

Fixes [Bug #15798]

thread_pthread.c

@@ -2187,25 +2187,33 @@ timer_pthread_fn(void *p)
     pthread_t main_thread_id = vm->main_thread->thread_id;
     struct pollfd pfd;
     int timeout = -1;
+    int ccp;
 
     pfd.fd = timer_pthread.low[0];
     pfd.events = POLLIN;
 
     while (system_working > 0) {
         (void)poll(&pfd, 1, timeout);
-        (void)consume_communication_pipe(pfd.fd);
+        ccp = consume_communication_pipe(pfd.fd);
 
-        if (system_working > 0 && ATOMIC_CAS(timer_pthread.armed, 1, 1)) {
-            pthread_kill(main_thread_id, SIGVTALRM);
+        if (system_working > 0) {
+	    if (ATOMIC_CAS(timer_pthread.armed, 1, 1)) {
+		pthread_kill(main_thread_id, SIGVTALRM);
 
-            if (rb_signal_buff_size() || !ubf_threads_empty()) {
-                timeout = TIME_QUANTUM_MSEC;
-            }
-            else {
-                ATOMIC_SET(timer_pthread.armed, 0);
-                timeout = -1;
-            }
-        }
+		if (rb_signal_buff_size() || !ubf_threads_empty()) {
+		    timeout = TIME_QUANTUM_MSEC;
+		}
+		else {
+		    ATOMIC_SET(timer_pthread.armed, 0);
+		    timeout = -1;
+		}
+	    }
+	    else if (ccp) {
+		pthread_kill(main_thread_id, SIGVTALRM);
+		ATOMIC_SET(timer_pthread.armed, 0);
+		timeout = -1;
+	    }
+	}
     }
 
     return 0;