Stabilize `core::ffi::CStr`, `alloc::ffi::CString`, and friends Stabilize the `core_c_str` and `alloc_c_string` feature gates. Change `std::ffi` to re-export these types rather than creating type aliases, since they now have matching stability.
core::ffi::CStr
alloc::ffi::CString
unused_macro_rules
std::alloc::System
#[rustc_deprecated]
lazy::Sync{OnceCell,Lazy}
sync::{Once,Lazy}Lock