output child WEXITSTATUS/WTERMSIG on abnormal termination

st.c

@@ -738,8 +738,10 @@ sigchld(int a)
 	if (pid != p)
 		return;
 
-	if (!WIFEXITED(stat) || WEXITSTATUS(stat))
-		die("child finished with error '%d'\n", stat);
+	if (WIFEXITED(stat) && WEXITSTATUS(stat))
+		die("child exited with status %d\n", WEXITSTATUS(stat));
+	else if (WIFSIGNALED(stat))
+		die("child terminated due to signal %d\n", WTERMSIG(stat));
 	exit(0);
 }