I've prepared a patch that allows additional syscalls on some architectures and pushed it to a branch in the debcargo-conf repo.
Rust-sniffglue is not a key package, so as I see it you have two possible ways forward here. The first is to upload the package as-is and file an unblock request justifying your changes to the release team. The second is to fix the autopkgtest. It's currently "neutral" due to a dependency on rust-boxxy which is not present in Debian. From taking a quick look it looks to me like any tests that rely on boxxy could probablly be patched out and the dev-dependency dropped to allow the remainder of the testsuite to run.
