Add sysb and sysc scaffolding.

Now that we have the Linux Kernel built, we move to a full-disk (rather
than initramfs) setup in sysc. However, we cannot assume the seed kernel
has support for mounting hard drives. So, first we need to kexec into
sysb, which is used as a jumping off point to create the hard drive for
sysc.

Additionally, since 2.6.16 does not have support for on-demand initramfs
(initramfs must be built into kernel), we will have to rebuild the linux
kernel within sysb without the initramfs.

All of this process is not performed for chroot mode. Instead, we skip
sysb and jump straight to sysc, copying over appropriate data.

The python scripts have been changed slightly. Each sys* inherits
SysGeneral, which contains various functions which are not specific to
any sys* and simplifies those files. rootfs now also handles sysb and
sysc.

bootstrap.cfg also gives an indication whether we are running in a
chroot to avoid attempting to kexec/mount within a chroot.

sysc/run.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/bash
+
+# SPDX-FileCopyrightText: 2021 Andrius Štikonas <andrius@stikonas.eu>
+# SPDX-FileCopyrightText: 2021 fosslinux <fosslinux@aussies.space>
+# SPDX-FileCopyrightText: 2021 Paul Dersey <pdersey@gmail.com>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+set -e
+
+. helpers.sh
+
+export PATH=/usr/bin:/usr/sbin
+export PREFIX=/usr
+export SOURCES=/usr/src
+
+create_fhs() {
+    # Add the rest of the FHS that we will use and is not created pre-boot
+    for d in bin lib sbin; do
+        ln -s "usr/${d}" "/${d}"
+    done
+    mkdir /etc /proc /run /sys /tmp /var
+    mount -t proc proc /proc
+    mount -t sysfs sysfs /sys
+    # Make /tmp a ramdisk (speeds up configure etc significantly)
+    mount -t tmpfs tmpfs /tmp
+}
+
+create_fhs
+
+build bash-5.1
+
+exec env -i PATH=${PATH} PREFIX=${PREFIX} SOURCES=${SOURCES} bash run2.sh