reewide: Purge all uses stdenv.system and top-level system

It is deprecated and will be removed after 18.09.

pkgs/build-support/build-fhs-userenv/env.nix

@@ -1,4 +1,4 @@
-{ stdenv, buildEnv, writeText, pkgs, pkgsi686Linux, system }:
+{ stdenv, buildEnv, writeText, pkgs, pkgsi686Linux }:
 
 { name, profile ? ""
 , targetPkgs ? pkgs: [], multiPkgs ? pkgs: []
@@ -22,7 +22,7 @@
 # /lib will link to /lib32
 
 let
-  is64Bit = system == "x86_64-linux";
+  is64Bit = stdenv.hostPlatform.parsed.cpu.bits == 64;
   isMultiBuild  = multiPkgs != null && is64Bit;
   isTargetBuild = !isMultiBuild;
 

pkgs/build-support/release/nix-build.nix

@@ -148,7 +148,7 @@ stdenv.mkDerivation (
     postPhases = postPhases ++ ["finalPhase"];
 
     meta = (if args ? meta then args.meta else {}) // {
-      description = if doCoverageAnalysis then "Coverage analysis" else "Nix package for ${stdenv.system}";
+      description = if doCoverageAnalysis then "Coverage analysis" else "Nix package for ${stdenv.hostPlatform.system}";
     };
 
   }

pkgs/build-support/vm/windows/controller/default.nix

@@ -157,7 +157,7 @@ let
     "-net vde,vlan=0,sock=$QEMU_VDE_SOCKET"
   ]);
 
-  maybeKvm64 = optional (stdenv.system == "x86_64-linux") "-cpu kvm64";
+  maybeKvm64 = optional (stdenv.hostPlatform.system == "x86_64-linux") "-cpu kvm64";
 
   cygwinQemuArgs = concatStringsSep " " (maybeKvm64 ++ [
     "-monitor unix:$MONITOR_SOCKET,server,nowait"

pkgs/build-support/vm/windows/cygwin-iso/default.nix

@@ -17,7 +17,7 @@ let
   };
 
   cygwinCross = (import ../../../../.. {
-    inherit (stdenv) system;
+    localSystem = stdenv.hostPlatform;
     crossSystem = {
       libc = "msvcrt";
       platform = {};