compositor: Use a virtual destructor when shutting down

Backend can now rely on their destroy function getting called on shutdown,
so reset tty etc there instead of handling SIGTERM twice.
diff --git a/compositor/compositor-drm.c b/compositor/compositor-drm.c
index e3e9b6f..1d04c06 100644
--- a/compositor/compositor-drm.c
+++ b/compositor/compositor-drm.c
@@ -42,9 +42,7 @@
 	struct udev *udev;
 	struct wl_event_source *drm_source;
 
-	struct wl_event_source *term_signal_source;
-
-        /* tty handling state */
+	/* tty handling state */
 	int tty_fd;
 	uint32_t vt_active : 1;
 
@@ -559,16 +557,6 @@
 	tcflush(ec->tty_fd, TCIFLUSH);
 }
 
-static void on_term_signal(int signal_number, void *data)
-{
-	struct drm_compositor *ec = data;
-
-	if (tcsetattr(ec->tty_fd, TCSANOW, &ec->terminal_attributes) < 0)
-		fprintf(stderr, "could not restore terminal to canonical mode\n");
-
-	exit(0);
-}
-
 static int setup_tty(struct drm_compositor *ec, struct wl_event_loop *loop)
 {
 	struct termios raw_attributes;
@@ -596,9 +584,6 @@
 	if (tcsetattr(ec->tty_fd, TCSANOW, &raw_attributes) < 0)
 		fprintf(stderr, "could not put terminal into raw mode: %m\n");
 
-	ec->term_signal_source =
-		wl_event_loop_add_signal(loop, SIGTERM, on_term_signal, ec);
-
 	ec->tty_input_source =
 		wl_event_loop_add_fd(loop, ec->tty_fd,
 				     WL_EVENT_READABLE, on_tty_input, ec);
@@ -631,6 +616,18 @@
 	return drmAuthMagic(ec->base.drm.fd, id);
 }
 
+static void
+drm_destroy(struct wlsc_compositor *ec)
+{
+	struct drm_compositor *d = (struct drm_compositor *) ec;
+
+	if (tcsetattr(d->tty_fd, TCSANOW, &d->terminal_attributes) < 0)
+		fprintf(stderr,
+			"could not restore terminal to canonical mode\n");
+
+	free(ec);
+}
+
 struct wlsc_compositor *
 drm_compositor_create(struct wl_display *display, int connector)
 {
@@ -691,6 +688,7 @@
 		wl_event_loop_add_fd(loop, ec->base.drm.fd,
 				     WL_EVENT_READABLE, on_drm_input, ec);
 	setup_tty(ec, loop);
+	ec->base.destroy = drm_destroy;
 	ec->base.authenticate = drm_authenticate;
 	ec->base.present = drm_compositor_present;
 	ec->base.focus = 1;
diff --git a/compositor/compositor-wayland.c b/compositor/compositor-wayland.c
index e289a29..fa630bc 100644
--- a/compositor/compositor-wayland.c
+++ b/compositor/compositor-wayland.c
@@ -507,6 +507,12 @@
 		wl_display_iterate(c->parent.display, WL_DISPLAY_WRITABLE);
 }
 
+static void
+wayland_destroy(struct wlsc_compositor *ec)
+{
+	free(ec);
+}
+
 struct wlsc_compositor *
 wayland_compositor_create(struct wl_display *display, int width, int height)
 {
@@ -556,6 +562,7 @@
 	if (c->parent.wl_source == NULL)
 		return NULL;
 
+	c->base.destroy = wayland_destroy;
 	c->base.authenticate = wayland_authenticate;
 	c->base.present = wayland_compositor_present;
 
diff --git a/compositor/compositor-x11.c b/compositor/compositor-x11.c
index 4cf9bf8..3aa2475 100644
--- a/compositor/compositor-x11.c
+++ b/compositor/compositor-x11.c
@@ -643,6 +643,12 @@
 	return dri2_authenticate((struct x11_compositor *) c, id);
 }
 
+static void
+x11_destroy(struct wlsc_compositor *ec)
+{
+	free(ec);
+}
+
 struct wlsc_compositor *
 x11_compositor_create(struct wl_display *display, int width, int height)
 {
@@ -686,6 +692,7 @@
 				     WL_EVENT_READABLE,
 				     x11_compositor_handle_event, c);
 
+	c->base.destroy = x11_destroy;
 	c->base.authenticate = x11_authenticate;
 	c->base.present = x11_compositor_present;
 
diff --git a/compositor/compositor.c b/compositor/compositor.c
index 28f16dd..a09f6d9 100644
--- a/compositor/compositor.c
+++ b/compositor/compositor.c
@@ -1452,5 +1452,7 @@
 
 	wl_display_destroy(display);
 
+	ec->destroy(ec);
+
 	return 0;
 }
diff --git a/compositor/compositor.h b/compositor/compositor.h
index a41bc64..85188f9 100644
--- a/compositor/compositor.h
+++ b/compositor/compositor.h
@@ -163,6 +163,7 @@
 
 	uint32_t focus;
 
+	void (*destroy)(struct wlsc_compositor *ec);
 	int (*authenticate)(struct wlsc_compositor *c, uint32_t id);
 	void (*present)(struct wlsc_compositor *c);
 };