nixos-generate-config: detect extlinux bootloader

nixos/modules/installer/tools/nixos-generate-config.pl

@@ -536,6 +536,13 @@ if ($showHardwareConfig) {
   # Use the systemd-boot EFI boot loader.
   boot.loader.systemd-boot.enable = true;
   boot.loader.efi.canTouchEfiVariables = true;
+EOF
+        } elsif (-e "/boot/extlinux") {
+            $bootLoaderConfig = <<EOF;
+  # Use the extlinux boot loader. (NixOS wants to enable GRUB by default)
+  boot.loader.grub.enable = false;
+  # Enables the generation of /boot/extlinux/extlinux.conf
+  boot.loader.generic-extlinux-compatible.enable = true;
 EOF
         } elsif ($virt ne "systemd-nspawn") {
             $bootLoaderConfig = <<EOF;