musl: 64-bit: Ensure proper (c)msghdr layout on big-endian
musl: 64-bit: Ensure proper (c)msghdr layout on big-endian

Discovered while debugging: djg/audioipc-2#52

rust-lang-nursery/libc,rust-lang/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang/libc,rust-lang-nursery/libc