liblaunch: implement stdio handle initialisation for child task

lib/liblaunch/include/launch.h

@@ -64,6 +64,8 @@ struct launch_parameters {
 	size_t p_channel_count;
 
 	void *p_resolver_arg;
+
+	kern_handle_t p_stdio[3];
 };
 
 struct launch_result {

lib/liblaunch/launch.c

@@ -209,6 +209,20 @@ enum launch_status launch_ctx_execute(
 		remote_stack_buf + STACK_SIZE);
 	virt_addr_t bsdata = write_bootstrap_data(&stack, interp_path, params);
 
+	for (int i = 0; i < 3; i++) {
+		if (params->p_stdio[i] == KERN_HANDLE_INVALID) {
+			continue;
+		}
+
+		kern_handle_transfer(
+			KERN_HANDLE_INVALID,
+			params->p_stdio[i],
+			remote_task,
+			i,
+			HANDLE_TRANSFER_MOVE,
+			NULL);
+	}
+
 	virt_addr_t ip = image.e_hdr.e_entry + image.e_remote_base;
 
 	kern_handle_t thread;