Enable ptrace on all Linux platforms

Nothing that nix currently binds is architecture-specific, and Android
supports ptrace just as much as non-Android Linux.

src/sys/mod.rs

@@ -52,11 +52,7 @@ pub mod uio;
 
 pub mod time;
 
-#[cfg(all(target_os = "linux",
-          any(target_arch = "x86",
-              target_arch = "x86_64",
-              target_arch = "arm")),
-          )]
+#[cfg(any(target_os = "linux", target_os = "android"))]
 pub mod ptrace;
 
 pub mod select;

src/sys/ptrace.rs

@@ -2,11 +2,6 @@ use std::{mem, ptr};
 use {Errno, Error, Result};
 use libc::{pid_t, c_void, c_long, siginfo_t};
 
-#[cfg(all(target_os = "linux",
-          any(target_arch = "x86",
-              target_arch = "x86_64",
-              target_arch = "arm")),
-          )]
 pub mod ptrace {
     use libc::c_int;