Do not depend on except for bootstrap

Author: spastorino

library/core/src/lib.rs

@@ -132,8 +132,8 @@
 #![feature(transparent_unions)]
 #![feature(try_blocks)]
 #![feature(unboxed_closures)]
-#![feature(unsized_locals)]
 #![cfg_attr(not(bootstrap), feature(unsized_fn_params))]
+#![cfg_attr(bootstrap, feature(unsized_locals))]
 #![cfg_attr(bootstrap, feature(untagged_unions))]
 #![feature(unwind_attributes)]
 #![feature(variant_count)]