segfault with x86_64 musl target

[brayniac]

The smoketest segfaults when built with the x86_64-unknown-linux-musl target. This would block support on Alpine and other musl libc based distributions or when building with musl toolchain on "normal" glibc based distributions.

Reported in rust-bpf/rust-bcc#166

x86_64-unknown-linux-musl is currently a tier 2 target for Rust (https://forge.rust-lang.org/release/platform-support.html)

I'd take a PR that addresses this, but I don't think we're going to support x86_64-unknown-linux-musl as tier 1 for the rust-bpf projects at this time.