Raise MSRV to 1.64 and delegate `ctypes` type aliases to `core::ffi`

[polarathene]

Just sharing this observation despite the benefit likely being minimal. Delegating the C FFI type aliases to those from core::ffi by bumping rust-version to 1.64 seems desirable?

It'd have avoided the need for PRs like this in March 2026 for example (which is merged but still unreleased).

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Details

Presently linux-raw-sys supports Rust 1.63 (Aug 2022) as a minimum (in May 2023 rust-version was bumped from 1.48 to benefit from improved const fn support):

linux-raw-sys/Cargo.toml

Line 13 in 3b15c17

rust-version = "1.63"

In Nov 2021 linux-raw-sys switched from a cty crate dep to vendoring it's own ctypes type alias module, which presently has required a bit of maintenance support over the past year for Tier 3 targets with ensuring the correct c_char (m68k, hexagon (as a follow-up to restoring support), MIPS R6).

Since Rust 1.64 (Sep 2022) the equivalent FFI C types have been available via the core crate (the target list is managed by a cfg_select! macro, and prior to that the cfg_if! crate macro).

Although this comment says core was not available for a m68k target? (unless they used rustc_codegen_gcc) but as core is already used elsewhere in this crate I assume that wouldn't equate to a regression 😅