Fix some clippy warnings (#1277)

cranelift/codegen/src/binemit/memorysink.rs

@@ -46,6 +46,8 @@ pub struct MemoryCodeSink<'a> {
 impl<'a> MemoryCodeSink<'a> {
     /// Create a new memory code sink that writes a function to the memory pointed to by `data`.
     ///
+    /// # Safety
+    ///
     /// This function is unsafe since `MemoryCodeSink` does not perform bounds checking on the
     /// memory buffer, and it can't guarantee that the `data` pointer is valid.
     pub unsafe fn new(