Deprecate top-level `{build,host,target}Platform`

overlay/default.nix

@@ -6,13 +6,13 @@ let
   # on whether the host or target system is Genode.
 
   overrideHost = attrs: drv:
-    if hostPlatform.isGenode then drv.override attrs else drv;
+    if stdenv.hostPlatform.isGenode then drv.override attrs else drv;
 
   overrideAttrsHost = f: drv:
-    if hostPlatform.isGenode then drv.overrideAttrs f else drv;
+    if stdenv.hostPlatform.isGenode then drv.overrideAttrs f else drv;
 
   overrideAttrsTarget = f: drv:
-    if targetPlatform.isGenode then drv.overrideAttrs f else drv;
+    if stdenv.targetPlatform.isGenode then drv.overrideAttrs f else drv;
 
   addPatches' = patches: attrs: { patches = attrs.patches or [ ] ++ patches; };
 
@@ -25,7 +25,7 @@ let
 
   nullPkgs =
     # Nullify these packages to find problems early.
-    if hostPlatform.isGenode then
+    if stdenv.hostPlatform.isGenode then
       builtins.listToAttrs (map (name: {
         inherit name;
         value = final.hello;
@@ -140,7 +140,7 @@ in nullPkgs // {
 
   linuxPackages =
     # Dummy package.
-    if hostPlatform.isGenode then {
+    if stdenv.hostPlatform.isGenode then {
       extend = _: final.linuxPackages;
       features = { };
       kernel = {
@@ -153,7 +153,7 @@ in nullPkgs // {
     } else
       prev.linuxPackages;
 
-  llvmPackages = if targetPlatform.isGenode then
+  llvmPackages = if stdenv.targetPlatform.isGenode then
     final.llvmPackages_11
   else
     prev.llvmPackages;
@@ -171,7 +171,7 @@ in nullPkgs // {
     # Packages from the Nimble flake with adjustments.
     prev.nimPackages.overrideScope' (final': prev':
       with final'; {
-        buildNimPackage = if hostPlatform.isGenode then
+        buildNimPackage = if stdenv.hostPlatform.isGenode then
           ({ nimFlags ? [ ], ... }@args:
             prev'.buildNimPackage (args // {
               nimBackend = "cpp";

packages/genodelabs/default.nix

@@ -4,7 +4,7 @@ let
   inherit (final) lib;
   inherit (prev.buildPackages) buildPackages;
 
-  platform = final.targetPlatform;
+  platform = final.stdenv.targetPlatform;
 
   arch = with platform;
     if isx86_64 then

packages/solo5/default.nix

@@ -28,7 +28,7 @@ in stdenv.mkDerivation {
   configurePhase = with stdenv; ''
     runHook preConfigure
     sh configure.sh
-    ${lib.optionalString (hostPlatform.isAarch64) "rm -fr tests/test_fpu"}
+    ${lib.optionalString (stdenv.hostPlatform.isAarch64) "rm -fr tests/test_fpu"}
     rm -fr tests/test_tls
     runHook postConfigure
   '';

tests/default.nix

@@ -23,7 +23,7 @@ let
       ];
 
       core = builtins.filter (core:
-        builtins.any (x: x == testPkgs.hostPlatform.system) core.platforms) [
+        builtins.any (x: x == testPkgs.stdenv.hostPlatform.system) core.platforms) [
           /* # Need to fix the QEMU boot parameters?
              {
                prefix = "hw-pc-";