Support swap files in qemu or bare-metal mode

This can help alleviate memory pressure when bootstrapping
with high core counts.

steps/improve/swap.sh

@@ -0,0 +1,19 @@
+
+#!/bin/sh
+#
+# SPDX-FileCopyrightText: 2024 Gábor Stefanik <netrolller.3d@gmail.com>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# Set up swap
+
+. /steps/bootstrap.cfg
+. /steps/env
+
+if ! test -f /swapfile
+then
+    echo "Making swap..."
+    dd if=/dev/zero of=/swapfile bs=1M count=${SWAP_SIZE}
+    mkswap /swapfile
+fi
+swapon /swapfile

steps/manifest

@@ -119,6 +119,7 @@ build: linux-4.9.10 ( BUILD_LINUX == True )
 jump: break ( INTERNAL_CI == pass1 )
 jump: linux ( CHROOT == False )
 improve: finalize_fhs
+improve: swap ( SWAP_SIZE != 0 )
 build: musl-1.2.4
 build: curl-8.5.0
 improve: populate_device_nodes