Set HAVE_USLEEP

SQLite otherwise has to sleep for a second at a time when waiting for a
lock (!)

libsqlite3-sys/build.rs

@@ -34,6 +34,7 @@ mod build {
             .flag("-DSQLITE_SOUNDEX")
             .flag("-DSQLITE_THREADSAFE=1")
             .flag("-DSQLITE_USE_URI")
+            .flag("-DHAVE_USLEEP=1")
             .compile("libsqlite3.a");
     }
 }