Resolve ptr_eq clippy lint

    error: use `std::ptr::eq` when comparing raw pointers
       --> serde_derive/src/de.rs:362:12
        |
    362 |         if field as *const Field == transparent_field as *const Field {
        |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::eq(field, transparent_field)`
        |
    note: the lint level is defined here
       --> serde_derive/src/lib.rs:18:9
        |
    18  | #![deny(clippy::all, clippy::pedantic)]
        |         ^^^^^^^^^^^
        = note: `#[deny(clippy::ptr_eq)]` implied by `#[deny(clippy::all)]`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_eq

serde_derive/src/de.rs

@@ -12,6 +12,7 @@ use internals::{attr, ungroup, Ctxt, Derive};
 use pretend;
 
 use std::collections::BTreeSet;
+use std::ptr;
 
 pub fn expand_derive_deserialize(input: &syn::DeriveInput) -> Result<TokenStream, Vec<syn::Error>> {
     let ctxt = Ctxt::new();
@@ -359,7 +360,7 @@ fn deserialize_transparent(cont: &Container, params: &Parameters) -> Fragment {
 
     let assign = fields.iter().map(|field| {
         let member = &field.member;
-        if field as *const Field == transparent_field as *const Field {
+        if ptr::eq(field, transparent_field) {
             quote!(#member: __transparent)
         } else {
             let value = match field.attrs.default() {