Since Rust 1.51.0, support for macro addr_of! has been stabilized[1],
and this provides a way to get a raw pointer without potential UB in
some cases.
Memoffset alreadly uses the feature at the pre-stablilized stage (the
macro was named as raw_const! then). Therefore, switch to use the
stablilized version (and name) if Rust 1.51.0 and above is used,
otherwise use the original fallback version, which works in a less
technically correct way.
[1]: https://github.com/rust-lang/rust/pull/72279
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Gilad Naaman