It is not currently possible to build safer_ffi on Rust nightly (rustc 1.75.0-nightly (e20cb7702 2023-10-12) at the time of me filing this issue).
The reason appears to be ambiguity between std::cfg_match (an unstable feature introduced in rust-lang/rust#115416) and safer_ffi::utils::macros::cfg_match.
According to the compiler, the ambiguity is introduced due to the wildcard use std::* here: