Back out rust 1.61.0 upgrade from fbcode and xplat

Summary:
This reverts the following stack of 4 diffs:

- {D36877131}
- {D36887647}
- {D36888466}
- {D36930916 (c4f0de9)}

until someone on the Rust team has a chance to investigate an extreme regression in compile time/memory, and we have either a workaround or a backported fix.

Reviewed By: zertosh, diliop

Differential Revision: D37023453

fbshipit-source-id: f7667041738fc3f0542e571fab578c422164de4c

Author: David Tolnay

gazebo_lint/src/clippy.rs

@@ -190,11 +190,11 @@ pub fn match_def_path(cx: &LateContext, did: DefId, syms: &[&str]) -> bool {
 /// Matches the given `ty` with generics to the given types and generic types
 pub fn match_ty_path(cx: &LateContext, ty: Ty, ty_path: &[&str], generic_tys: &[&[&str]]) -> bool {
     if let TyKind::Adt(ty, subst) = ty.kind() {
-        if match_def_path(cx, ty.did(), ty_path) {
+        if match_def_path(cx, ty.did, ty_path) {
             let mut i = 0;
             while i < generic_tys.len() {
                 if let Some(ty_param) = subst.type_at(i).ty_adt_def() {
-                    if !match_def_path(cx, ty_param.did(), generic_tys[i]) {
+                    if !match_def_path(cx, ty_param.did, generic_tys[i]) {
                         return false;
                     } else {
                         i += 1;

gazebo_lint/src/lib.rs

@@ -428,7 +428,7 @@ fn check_impl_dupe(cx: &LateContext, item: &Item) {
     ) -> bool {
         match self_tys.kind() {
             TyKind::Adt(self_adt, sub) => {
-                for variant in self_adt.variants() {
+                for variant in self_adt.variants.iter() {
                     let mut fields = variant.fields.iter();
                     if let Some(field) = fields.next() {
                         if fields.next().is_some() {