Warnings about deprecated atomic initializers

[joshtriplett]

The generated code produces warnings about the use of deprecated atomic initializers:

warning: use of deprecated item 'std::sync::atomic::ATOMIC_BOOL_INIT': the `new` function is now preferred
 --> D:\a\libz-sys\libz-sys\target\x86_64-pc-windows-gnu\debug\build\systest-47d2caa40185cb8b\out/all.rs:4:49
  |
4 |             use std::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
  |                                                 ^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(deprecated)]` on by default

warning: use of deprecated item 'std::sync::atomic::ATOMIC_USIZE_INIT': the `new` function is now preferred
 --> D:\a\libz-sys\libz-sys\target\x86_64-pc-windows-gnu\debug\build\systest-47d2caa40185cb8b\out/all.rs:5:50
  |
5 |             use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT};
  |                                                  ^^^^^^^^^^^^^^^^^

warning: use of deprecated item 'std::sync::atomic::ATOMIC_BOOL_INIT': the `new` function is now preferred
  --> D:\a\libz-sys\libz-sys\target\x86_64-pc-windows-gnu\debug\build\systest-47d2caa40185cb8b\out/all.rs:41:41
   |
41 |             static FAILED: AtomicBool = ATOMIC_BOOL_INIT;
   |                                         ^^^^^^^^^^^^^^^^ help: replace the use of the deprecated item: `AtomicBool::new(false)`

warning: use of deprecated item 'std::sync::atomic::ATOMIC_USIZE_INIT': the `new` function is now preferred
  --> D:\a\libz-sys\libz-sys\target\x86_64-pc-windows-gnu\debug\build\systest-47d2caa40185cb8b\out/all.rs:42:42
   |
42 |             static NTESTS: AtomicUsize = ATOMIC_USIZE_INIT;
   |                                          ^^^^^^^^^^^^^^^^^ help: replace the use of the deprecated item: `AtomicUsize::new(0)`