Do not intern NUL terminators

The C representation needed by LLVM requires strings to be
NUL-terminated, but on the Rust side they should not contain unwanted
NULs.

src/librustc_driver/target_features.rs

@@ -49,7 +49,7 @@ pub fn add_configuration(cfg: &mut ast::CrateConfig, sess: &Session) {
     let tf = InternedString::new("target_feature");
     for feat in whitelist {
         if unsafe { LLVMRustHasFeature(target_machine, feat.as_ptr() as *const c_char) } {
-            cfg.push(attr::mk_name_value_item_str(tf.clone(), intern(feat)))
+            cfg.push(attr::mk_name_value_item_str(tf.clone(), intern(&feat[..feat.len()-1])))
         }
     }
 }