base: fix clang warning for void cast of retval

This path fixes a void cast used to silence unused return value warning.
Its a common pattern to use void cast to do that. The code uses void *
cast instead. It works for GCC, but clang complains about this.

Issue #3938

repos/base/src/lib/startup/init_main_thread.cc

@@ -104,7 +104,7 @@ extern "C" void init_main_thread()
 	 * Explicitly setup program environment at this point to ensure that its
 	 * destructor won't be registered for the atexit routine.
 	 */
-	(void*)env_deprecated();
+	(void)env_deprecated();
 	init_log(*env_deprecated()->parent());
 
 	/* create a thread object for the main thread */