std: Migrate to the new libc

* Delete `sys::unix::{c, sync}` as these are now all folded into libc itself
* Update all references to use `libc` as a result.
* Update all references to the new flat namespace.
* Moves all windows bindings into sys::c

src/liballoc_jemalloc/lib.rs

@@ -14,6 +14,7 @@
 #![staged_api]
 #![no_std]
 #![cfg_attr(not(stage0), allocator)]
+#![cfg_attr(stage0, allow(improper_ctypes))]
 #![unstable(feature = "alloc_jemalloc",
             reason = "this library is unlikely to be stabilized in its current \
                       form or name",