Add fake_read() to clippy

clippy_utils/src/usage.rs

@@ -7,6 +7,7 @@ use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
 use rustc_hir::{Expr, ExprKind, HirId, Path};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::LateContext;
+use rustc_middle::mir::FakeReadCause;
 use rustc_middle::hir::map::Map;
 use rustc_middle::ty;
 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
@@ -77,6 +78,8 @@ impl<'tcx> Delegate<'tcx> for MutVarsDelegate {
     fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, _: HirId) {
         self.update(&cmt)
     }
+
+    fn fake_read(&mut self, _: rustc_typeck::expr_use_visitor::Place<'tcx>, _: FakeReadCause) { }
 }
 
 pub struct ParamBindingIdCollector {