cmsg test program dumps core on s390x-unknown-linux-gnu

[asomers]

PR #1235 adds a new test program to make sure that the cmsg(3) family of macros are correctly implemented. But on s390x (in qemu, of course), it fails with the cryptic error message timeout: the monitored command dumped core. It seems as though the kernel hasn't even finished booting. I only see this error in Travis. On my desktop, cmsg works fine for s390x.

https://travis-ci.com/rust-lang/libc/jobs/175199672