Pass argc pointer to parse_options()

This lets us keep argc up to date as the backend picks out arguments
from the argv array.
diff --git a/src/compositor.h b/src/compositor.h
index fdde762..11afbb9 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -714,7 +714,7 @@
 
 int
 weston_compositor_init(struct weston_compositor *ec, struct wl_display *display,
-		       int argc, char *argv[], const char *config_file);
+		       int *argc, char *argv[], const char *config_file);
 void
 weston_compositor_shutdown(struct weston_compositor *ec);
 void
@@ -839,8 +839,8 @@
 noop_renderer_init(struct weston_compositor *ec);
 
 struct weston_compositor *
-backend_init(struct wl_display *display, int argc, char *argv[],
-	    const char *config_file);
+backend_init(struct wl_display *display, int *argc, char *argv[],
+	     const char *config_file);
 
 int
 module_init(struct weston_compositor *compositor);