build: fix building js2c with GN

This is a follow-up to nodejs#51605.

PR-URL: nodejs#51818
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz.nizipli@sentry.io>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

unofficial.gni

@@ -266,7 +266,10 @@ template("node_gn_build") {
     sources = [
       "tools/js2c.cc",
       "tools/executable_wrapper.h",
+      "src/embedded_data.cc",
+      "src/embedded_data.h",
     ]
+    include_dirs = [ "src" ]
   }
 
   action("run_node_js2c") {