fix build issue with function signature missing the cordova variable name; also avoid a warning

(cherry picked from commit d6f921f7fa178388cf4cb353f32d38b50bd5959d)
diff --git a/src/coreplugins.cpp b/src/coreplugins.cpp
index fc1a115..ebae0f6 100644
--- a/src/coreplugins.cpp
+++ b/src/coreplugins.cpp
@@ -27,6 +27,7 @@
 extern "C" {
 
 Q_DECL_EXPORT QList<QSharedPointer<CPlugin>> cordovaGetPluginInstances(Cordova *cordova) {
+    Q_UNUSED(cordova);
     QList<QSharedPointer<CPlugin>> res;
 
     INSERT_PLUGIN_HERE