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/shared/config-parser.h b/shared/config-parser.h
index 7fa9c3f..314057a 100644
--- a/shared/config-parser.h
+++ b/shared/config-parser.h
@@ -67,7 +67,7 @@
 
 int
 parse_options(const struct weston_option *options,
-	      int count, int argc, char *argv[]);
+	      int count, int *argc, char *argv[]);
 
 #endif /* CONFIGPARSER_H */