Use const fn to abstract away the contents of UnsafeCell & friends.

src/librustc/middle/infer/region_inference/graphviz.rs

@@ -32,7 +32,7 @@ use std::env;
 use std::fs::File;
 use std::io;
 use std::io::prelude::*;
-use std::sync::atomic::{AtomicBool, Ordering, ATOMIC_BOOL_INIT};
+use std::sync::atomic::{AtomicBool, Ordering};
 use syntax::ast;
 
 fn print_help_message() {
@@ -76,7 +76,7 @@ pub fn maybe_print_constraints_for<'a, 'tcx>(region_vars: &RegionVarBindings<'a,
     let output_path = {
         let output_template = match requested_output {
             Ok(ref s) if &**s == "help" => {
-                static PRINTED_YET: AtomicBool = ATOMIC_BOOL_INIT;
+                static PRINTED_YET: AtomicBool = AtomicBool::new(false);
                 if !PRINTED_YET.load(Ordering::SeqCst) {
                     print_help_message();
                     PRINTED_YET.store(true, Ordering::SeqCst);