Auto merge of #1089 - xd009642:apple_ptrace, r=alexcrichton
Auto merge of #1089 - xd009642:apple_ptrace, r=alexcrichton

Added ptrace constants for apple

I noticed the ptrace constants were missing for apple so I've added them referencing this [header](https://opensource.apple.com/source/xnu/xnu-792.13.8/bsd/sys/ptrace.h). This doesn't add any new functions just constants so I haven't added any tests which seems to be correct.

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