[build] Consider FIDL public deps when exporting libraries to the GN build.

Change-Id: I5e2de81512086995ef6fb6d2e62492c41a868e57
diff --git a/zircon/public/gn/BUILDCONFIG.gn b/zircon/public/gn/BUILDCONFIG.gn
index 5027ae5..1c07690 100644
--- a/zircon/public/gn/BUILDCONFIG.gn
+++ b/zircon/public/gn/BUILDCONFIG.gn
@@ -420,7 +420,9 @@
             get_path_info(get_label_info(label, "name"), "extension") ==
             "headers" ||
             get_path_info(get_label_info(label, "dir"), "dir") ==
-            "$zx/system/banjo") {
+            "$zx/system/banjo" ||
+            get_path_info(get_label_info(label, "dir"), "dir") ==
+            "$zx/system/fidl") {
           sdk_deps += [ label ]
         }
       }