Fix unused macro warning when compiling tests without trace feature.

tests/config_log.rs

@@ -1,6 +1,7 @@
 //! This file contains unit tests for rusqlite::trace::config_log. This function affects
 //! SQLite process-wide and so is not safe to run as a normal #[test] in the library.
 
+#[cfg(feature = "trace")]
 #[macro_use]
 extern crate lazy_static;
 extern crate rusqlite;