Handle dlsym() failures in chainloaders better

If these ever fail (because the function names change, not that that
should happen anytime soon) then you'll now get the expected logging
output instead of it just printing an assertion failure to the terminal.

src/chainloader/utils.h

@@ -37,3 +37,10 @@
  *   directories in case `ldconfig` was not set up correctly.
  */
 void* find_plugin_library(const std::string& name);
+
+/**
+ * Log a message when a `dlsym()` call fails and show a corresponding desktop
+ * notification. Used as part of the `LOAD_FUNCTION` macros.
+ */
+void log_failing_dlsym(const std::string& library_name,
+                       const char* function_name);