Fix error E0460 when compiled on Rustc repo

Author: tesuji

tests/compile-test.rs

@@ -56,6 +56,7 @@ fn default_config() -> compiletest::Config {
         build_info.host_lib().join("test_build_base")
     };
     config.rustc_path = build_info.clippy_driver_path();
+    config.clean_rmeta();
     config
 }