release.nix: resurrect stdenvBootstrapTools

13d6681ce7 crippled it unintentionally.
Also remove the incorrect/non-existing stdenv.i686-linux;
building the bootstrap tools should be a good-enough test anyway.

pkgs/top-level/release.nix

···
               jobs.manual
               jobs.lib-tests
               jobs.stdenv.x86_64-linux
-              jobs.stdenv.i686-linux # most basic sanity check
               jobs.stdenv.x86_64-darwin
               jobs.linux.x86_64-linux
               jobs.python.x86_64-linux
···
               jobs.vim.x86_64-darwin
             ] ++ lib.collect lib.isDerivation jobs.stdenvBootstrapTools;
         };
-    } // (lib.optionalAttrs (builtins.elem "i686-linux" systemsWithAnySupport) {
-      stdenvBootstrapTools.i686-linux =
-        { inherit (import ../stdenv/linux/make-bootstrap-tools.nix { system = "i686-linux"; }) dist test; };
-    }) // (lib.optionalAttrs (builtins.elem "x86_64-linux" systemsWithAnySupport) {
-      stdenvBootstrapTools.x86_64-linux =
-        { inherit (import ../stdenv/linux/make-bootstrap-tools.nix { system = "x86_64-linux"; }) dist test; };
-    }) // (lib.optionalAttrs (builtins.elem "aarch64-linux" systemsWithAnySupport) {
-      stdenvBootstrapTools.aarch64-linux =
-        { inherit (import ../stdenv/linux/make-bootstrap-tools.nix { system = "aarch64-linux"; }) dist test; };
-    }) // (lib.optionalAttrs (builtins.elem "x86_64-darwin" systemsWithAnySupport) {
-      stdenvBootstrapTools.x86_64-darwin =
-        let
-          bootstrap = import ../stdenv/darwin/make-bootstrap-tools.nix { system = "x86_64-darwin"; };
-        in {
-          # Lightweight distribution and test
-          inherit (bootstrap) dist test;
-          # Test a full stdenv bootstrap from the bootstrap tools definition
-          inherit (bootstrap.test-pkgs) stdenv;
-        };
-    }) // (mapTestOn ((packagePlatforms pkgs) // rec {
+
+      stdenvBootstrapTools = with lib;
+        genAttrs systemsWithAnySupport
+          (system: {
+            inherit (import ../stdenv/linux/make-bootstrap-tools.nix { inherit system; })
+              dist test;
+          })
+        # darwin is special in this
+        // optionalAttrs (builtins.elem "x86_64-darwin" systemsWithAnySupport) {
+          x86_64-darwin =
+            let
+              bootstrap = import ../stdenv/darwin/make-bootstrap-tools.nix { system = "x86_64-darwin"; };
+            in {
+              # Lightweight distribution and test
+              inherit (bootstrap) dist test;
+              # Test a full stdenv bootstrap from the bootstrap tools definition
+              inherit (bootstrap.test-pkgs) stdenv;
+            };
+          };
+
+    } // (mapTestOn ((packagePlatforms pkgs) // rec {
       haskell.compiler = packagePlatforms pkgs.haskell.compiler;
       haskellPackages = packagePlatforms pkgs.haskellPackages;