flake: export layers, update make_msys_packages for flakes

flake.nix

@@ -888,6 +888,7 @@
 
       inherit utils;
       inherit makeWindowsImage;
+      inherit layers;
 
       demo-ssh = utils.wfvm-run {
         name = "demo-ssh";

layers/make_msys_packages.sh

@@ -2,27 +2,7 @@
 
 set -e
 
-nix-build -E "
-let
-  pkgs = import <nixpkgs> {};
-  wfvm = import ../default.nix { inherit pkgs; };
-in
-  wfvm.utils.wfvm-run {
-    name = \"get-msys-packages\";
-    image = wfvm.makeWindowsImage { installCommands = [ wfvm.layers.msys2 ]; };
-    script = ''
-      cat > getmsyspackages.bat << EOF
-      set MSYS=C:\\MSYS64
-      set TOOLPREF=mingw-w64-x86_64-
-      set PATH=%MSYS%\usr\bin;%MSYS%\mingw64\bin;%PATH%
-      pacman -Sp %TOOLPREF%gcc %TOOLPREF%binutils make autoconf automake libtool texinfo > packages.txt
-      EOF
-      \${wfvm.utils.win-put}/bin/win-put getmsyspackages.bat
-      \${wfvm.utils.win-exec}/bin/win-exec getmsyspackages
-      \${wfvm.utils.win-get}/bin/win-get packages.txt
-    '';
-  }
-"
+nix build .#make-msys-packages
 
 ./result/bin/wfvm-run-get-msys-packages