Add ENOTSUP to Linux and Android

While ENOTSUP is defined as equal to EOPNOTSUPP on these platforms,
exposing the ENOTSUP symbol (as libc does) allows for writing portable
code that may want to reference this error code.

CHANGELOG.md

@@ -34,6 +34,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#952](https://github.com/nix-rust/nix/pull/952))
 - Added the `time_t` and `suseconds_t` public aliases within `sys::time`.
   ([#968](https://github.com/nix-rust/nix/pull/968))
+- Added ENOTSUP errno support for Linux and Android.
+  ([#969](https://github.com/nix-rust/nix/pull/969))
 
 ### Changed
 - Increased required Rust version to 1.24.1

src/errno.rs

@@ -674,6 +674,7 @@ mod consts {
 
     pub const EWOULDBLOCK: Errno = Errno::EAGAIN;
     pub const EDEADLOCK:   Errno = Errno::EDEADLK;
+    pub const ENOTSUP:     Errno = Errno::EOPNOTSUPP;
 
     pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;