At --log-warnings=9 or more, log at what address a dynamic plugin was loaded.

It helps to interpret valgrind/safemalloc memory-related warnings that are
printed when a plugin is unloaded (and thus cannot resolve addresses automatically)

sql/sql_plugin.cc

@@ -1357,6 +1357,16 @@ static int plugin_initialize(MEM_ROOT *tmp_root, struct st_plugin_int *plugin,
     goto err;
   }
 
+  if (plugin->plugin_dl && global_system_variables.log_warnings >= 9)
+  {
+    void *sym= dlsym(plugin->plugin_dl->handle,
+                     plugin->plugin_dl->mariaversion ?
+                       maria_plugin_declarations_sym : plugin_declarations_sym);
+    DBUG_ASSERT(sym);
+    sql_print_information("Plugin %s loaded at %p",
+                          plugin->name.str, sym);
+  }
+
   if (plugin_type_initialize[plugin->plugin->type])
   {
     if ((*plugin_type_initialize[plugin->plugin->type])(plugin))