fio: 2.2.11 -> 2.9

This fixes the build against linux 4.4 headers; see
https://hydra.nixos.org/build/35697941/log/raw

Also set `platforms.unix` per what upstream claims.

pkgs/tools/system/fio/default.nix

···
 { stdenv, fetchFromGitHub, libaio, python, zlib }:
 
-let version = "2.2.11"; in
+let
+  version = "2.9";
+  sha256 = "10x5b1f1pdsh33kqzc8yf2v4mijlmkh72lmh9za6kz7hb3hp1nvi";
+in
 
 stdenv.mkDerivation rec {
   name = "fio-${version}";
···
     owner = "axboe";
     repo = "fio";
     rev = "fio-${version}";
-    sha256 = "0g26xvbb60f96ks8q7jpap0xc2grb5j5w4m4glz910ndgf0s45wm";
+    inherit sha256;
   };
 
   buildInputs = [ libaio python zlib ];
···
     homepage = "http://git.kernel.dk/?p=fio.git;a=summary";
     description = "Flexible IO Tester - an IO benchmark tool";
     license = licenses.gpl2;
-    platforms = platforms.linux;
+    platforms = platforms.unix;
   };
 }