Add version of Nix that's patched for low-RAM environments

morepkgs/default.nix

@@ -2,5 +2,6 @@ self: super:
 	{
 		morepkgs = {
 			xonotic = super.callPackage ./pkgs/games/xonotic {};
+			low-ram-nix = super.callPackage ./pkgs/system/low-ram-nix {};
 		};
 	}

morepkgs/pkgs/system/low-ram-nix/default.nix

@@ -0,0 +1,25 @@
+/* Source: https://github.com/NixOS/nix/pull/2206#issuecomment-394130511 */
+
+{nixUnstable, fetchpatch, fetchFromGitHub, aws-sdk-cpp, ...}:
+	nixUnstable.overrideAttrs (oldAttrs: {
+		src = fetchFromGitHub {
+			owner = "NixOS";
+			repo = "nix";
+			rev = "54b1c596435b0aaf3a2557652ad4bf74d5756514";
+			sha256 = "0g7knsfj445r50rk0d9hm5n1pv20k542bz6xf5c47qmkgvfa40x4";
+		};
+		patches = [
+			(fetchpatch {
+				url = "https://github.com/nh2/nix/commit/d31a4410d92790e2c27110154896445d99d7abfe.patch";
+				sha256 = "08gcw2xw8yc61zz2nr1j3cnd6wagp5qs02mjfazrd9wa045y26hg";
+			})
+		];
+		# Changes cherry-picked from upstream nix `release-common.nix` that
+		# aren't in `pkgs.nixUnstable` yet:
+		buildInputs = oldAttrs.buildInputs ++ [
+			(aws-sdk-cpp.override {
+				apis = ["s3" "transfer"];
+				customMemoryManagement = false;
+			})
+		];
+	})