plugins: python renderer: Fix broken code due to merge. Functions of plugins now have to be exported explicitly.

include/gds-render/output-renderers/external-renderer-interfaces.h

@@ -18,6 +18,11 @@
  */
 #define EXPORT_FUNC __attribute__((visibility("default")))
 
+/**
+ * @brief This define is used to export a variable symbol from a shared object
+ */
+#define EXPORT_VAR EXPORT_FUNC
+
 /**
  * @brief Function name expected to be found in external library for rendering.
  *
@@ -63,8 +68,10 @@
 
 /**
  * @brief Define for declaring exported variables
+ *
+ * This not only helps with the declaration but also makes the symbols visible, so they can be accessed form outside the library
  */
-#define VAR_DECL(VAR) VAR
+#define EXPORTED_VAR_DECL(VAR) EXPORT_VAR VAR
 
 /** @} */