Add fnl build target

mojo/tools/embed/rules.gni

Index: mojo/tools/embed/rules.gni
diff --git a/mojo/tools/embed/rules.gni b/mojo/tools/embed/rules.gni
index 6171812669126039d0104c0fb0e6acdb85c7832c..c4c806049e3351565f649cf67e8c8bddbbd96126 100644
--- a/mojo/tools/embed/rules.gni
+++ b/mojo/tools/embed/rules.gni
@@ -35,6 +35,11 @@ template("embed_file") {
     }
   }
 
+  config_target_name = "__${target_name}_config"
+  config(config_target_name) {
+    cflags = [ "-Wno-narrowing" ]
+  }
+
   source_set(target_name) {
     sources = generator_outputs
 
@@ -42,6 +47,8 @@ template("embed_file") {
       testonly = invoker.testonly
     }
 
+    configs += [ ":${config_target_name}" ]
+
     deps = [
       ":${generator_target_name}",
     ]