modules/workaround-make: add workaround for make

See #91 for context.

modules/module-list.nix

@@ -14,5 +14,6 @@
   ./time.nix
   ./user.nix
   ./version.nix
+  ./workaround-make.nix
   <nixpkgs/nixos/modules/misc/assertions.nix>
 ]

modules/workaround-make.nix

@@ -0,0 +1,70 @@
+# Copyright (c) 2019-2020, see AUTHORS. Licensed under MIT License, see LICENSE.
+
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.system.workaround.make-posix-spawn;
+
+  gnumake-no-posix-spawn = pkgs.gnumake.overrideAttrs (old: {
+    configureFlags = old.configureFlags ++ [ "--disable-posix-spawn" ];
+
+    buildPhase = "${pkgs.gnumake42}/bin/make";
+    installPhase = ''
+      mkdir -p $out
+      ${pkgs.gnumake42}/bin/make install
+    '';
+
+    # make a copy to facilitate repairs when it gets broken
+    # because of being bind-mounted onto the normal make
+    postFixup = ''
+      cp $out/bin/make $out/bin/overlaying-make
+      touch $out/SEE_system.workaround.make-posix-spawn.enable
+    '';
+  });
+in
+{
+
+  ###### interface
+
+  options = {
+
+    system.workaround.make-posix-spawn.enable = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        On some devices, GNU make 4.3 fails with 'Function not implemented',
+        and the workaround is to compile it with '--disable-posix-spawn'.
+        This option will shadow the original make in a really dirty way,
+        by overlaying broken gnumake with a fixed version on proot level.
+        Please only enable this for a limited time:
+        get stuck with a broken build; stop attempting to build something;
+        enable the option; nix-on-droid switch, relogin, build,
+        disable the option; nix-on-droid switch, relogin.
+
+        If you leave it on Nix-store validation will fail,
+        repairs will break the working make,
+        updates will do bad things. You have been warned.
+
+        Consider building remotely as an alternative for such devices:
+        https://github.com/t184256/nix-on-droid/wiki/Remote-building
+      '';
+    };
+
+  };
+
+  ###### implementation
+
+  config = {
+    build.extraProotOptions =
+      lib.optionals cfg.enable [
+        "-b"
+        (
+          "${config.build.installationDir}/"
+          + "${gnumake-no-posix-spawn}/bin/overlaying-make"
+          + ":${pkgs.gnumake}/bin/make"
+        )
+      ];
+  };
+}