Fix RefUnwindSafe & UnwinsSafe impls for lazy::SyncLazy
Fix RefUnwindSafe & UnwinsSafe impls for lazy::SyncLazy

The logic here is the same as for Send&Sync impls.

graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust