Build the same configuration when compiling and for --print cfg

The configuration returned by `config::build_configuration` needs to
be modified with `target_features::add_configuration` in order to also
contain the target features. This is already done for the
configuration used when compiling and when creating the documentation,
but was missing in the `cfg` printing code.

src/librustc_driver/lib.rs

@@ -565,7 +565,9 @@ impl RustcDefaultCalls {
                     }
                 }
                 PrintRequest::Cfg => {
-                    for cfg in config::build_configuration(sess) {
+                    let mut cfg = config::build_configuration(&sess);
+                    target_features::add_configuration(&mut cfg, &sess);
+                    for cfg in cfg {
                         match cfg.node {
                             ast::MetaItemKind::Word(ref word) => println!("{}", word),
                             ast::MetaItemKind::NameValue(ref name, ref value) => {