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-headless.c b/src/compositor-headless.c
index 03bd0a4..1e286fa 100644
--- a/src/compositor-headless.c
+++ b/src/compositor-headless.c
@@ -152,7 +152,7 @@
 static struct weston_compositor *
 headless_compositor_create(struct wl_display *display,
 			  int width, int height, const char *display_name,
-			  int argc, char *argv[], const char *config_file)
+			  int *argc, char *argv[], const char *config_file)
 {
 	struct headless_compositor *c;
 
@@ -187,7 +187,7 @@
 }
 
 WL_EXPORT struct weston_compositor *
-backend_init(struct wl_display *display, int argc, char *argv[],
+backend_init(struct wl_display *display, int *argc, char *argv[],
 	     const char *config_file)
 {
 	int width = 1024, height = 640;