boehmgc_{nix,nixUnstable}: Move into {nix,nixUnstable}.passthru

Do not pollute top-level, but do provide allow the derivations to
be accessed for debugging and reuse if necessary.

pkgs/tools/package-management/nix/default.nix

@@ -2,8 +2,7 @@
 , storeDir ? "/nix/store"
 , stateDir ? "/nix/var"
 , confDir ? "/etc"
-, boehmgc_nix
-, boehmgc_nixUnstable
+, boehmgc
 , Security
 }:
 
@@ -194,10 +193,25 @@ common =
 
           preBuild = "unset NIX_INDENT_MAKE";
         });
+        inherit boehmgc;
       };
     };
   in nix;
 
+  boehmgc_nix = boehmgc.override {
+    enableLargeConfig = true;
+  };
+
+  boehmgc_nixUnstable = boehmgc_nix.overrideAttrs (drv: {
+    patches = (drv.patches or []) ++ [
+      # Part of the GC solution in https://github.com/NixOS/nix/pull/4944
+      (fetchpatch {
+        url = https://github.com/hercules-ci/nix/raw/5c58d84a76d96f269e3ff1e72c9c9ba5f68576af/boehmgc-coroutine-sp-fallback.diff;
+        sha256 = "sha256-JvnWVTlkltmQUs/0qApv/LPZ690UX1/2hEP+LYRwKbI=";
+      })
+    ];
+  });
+
 in rec {
 
   nix = nixStable;

pkgs/top-level/all-packages.nix

@@ -14669,18 +14669,6 @@ in
 
   boehmgc = callPackage ../development/libraries/boehm-gc { };
   boehmgc_766 = callPackage ../development/libraries/boehm-gc/7.6.6.nix { };
-  boehmgc_nix = pkgs.boehmgc.override {
-    enableLargeConfig = true;
-  };
-  boehmgc_nixUnstable = pkgs.boehmgc_nix.overrideAttrs (drv: {
-    patches = (drv.patches or []) ++ [
-      # Part of the GC solution in https://github.com/NixOS/nix/pull/4944
-      (pkgs.fetchpatch {
-        url = https://github.com/hercules-ci/nix/raw/5c58d84a76d96f269e3ff1e72c9c9ba5f68576af/boehmgc-coroutine-sp-fallback.diff;
-        sha256 = "sha256-JvnWVTlkltmQUs/0qApv/LPZ690UX1/2hEP+LYRwKbI=";
-      })
-    ];
-  });
 
   boolstuff = callPackage ../development/libraries/boolstuff { };