Make the `c` feature for `compiler-builtins` an explicit opt-in Its build script doesn't support cross-compilation. I tried fixing it, but the cc crate itself doesn't appear to support cross-compiling to windows either unless you use the -gnu toolchain: ``` error occurred: Failed to find tool. Is `lib.exe` installed? ``` Fixes https://github.com/rust-lang/rust/issues/101172.