Auto merge of #1393 - Susurrus:ptrace_detach, r=gnzlbg

Re-add PTRACE_DETACH for mips64 GNU targets

During the refactor in 4bd419e, `PTRACE_DETACH` was accidentally removed on
these targets. This re-adds it.

Fixes brokenness encountered during nix-rust/nix#1035

CC @asomers

src/unix/linux_like/linux/gnu/b64/mips64.rs

@@ -831,6 +831,7 @@ pub const TCSAFLUSH: ::c_int = 0x5410;
 
 pub const PTRACE_GETFPREGS: ::c_uint = 14;
 pub const PTRACE_SETFPREGS: ::c_uint = 15;
+pub const PTRACE_DETACH: ::c_uint = 17;
 pub const PTRACE_GETFPXREGS: ::c_uint = 18;
 pub const PTRACE_SETFPXREGS: ::c_uint = 19;
 pub const PTRACE_GETREGS: ::c_uint = 12;