Bump buildroot to 2020.11-rc1 (#985)

* Update buildroot-patches for 2020.11-rc1 buildroot

* Update buildroot to 2020.11-rc1

Signed-off-by: Stefan Agner <stefan@agner.ch>

* Don't rely on sfdisk --list-free output

The --list-free (-F) argument does not allow machine readable mode. And
it seems that the output format changes over time (different spacing,
using size postfixes instead of raw blocks).

Use sfdisk json output and calculate free partition space ourselfs. This
works for 2.35 and 2.36 and is more robust since we rely on output which
is meant for scripts to parse.

* Migrate defconfigs for Buildroot 2020.11-rc1

In particular, rename BR2_TARGET_UBOOT_BOOT_SCRIPT(_SOURCE) to
BR2_PACKAGE_HOST_UBOOT_TOOLS_BOOT_SCRIPT(_SOURCE).

* Rebase/remove systemd patches for systemd 246

* Drop apparmor/libapparmor from buildroot-external

* hassos-persists: use /run as directory for lockfiles

The U-Boot tools use /var/lock by default which is not created any more
by systemd by default (it is under tmpfiles legacy.conf, which we no
longer install).

* Disable systemd-update-done.service

The service is not suited for pure read-only systems. In particular the
service needs to be able to write a file in /etc and /var. Remove the
service. Note: This is a static service and cannot be removed using
systemd-preset.

* Disable apparmor.service for now

The service loads all default profiles. Some might actually cause
problems. E.g. the profile for ping seems not to match our setup for
/etc/resolv.conf:
[85503.634653] audit: type=1400 audit(1605286002.684:236): apparmor="DENIED" operation="open" profile="ping" name="/run/resolv.conf" pid=27585 comm="ping" requested_mask="r" denied_mask="r" fsuid=0 ouid=0

buildroot/docs/manual/using-buildroot-toolchain.txt

@@ -32,3 +32,17 @@ the tarball (e.g. because you will just be moving the +host+ directory,
 or will be generating the tarball on your own), Buildroot also allows
 you to just prepare the SDK with +make prepare-sdk+ without actually
 generating a tarball.
+
+For your convenience, by selecting the option
++BR2_PACKAGE_HOST_ENVIRONMENT_SETUP+, you can get a
++setup-environment+ script installed in +output/host/+ and therefore
+in your SDK.  This script can be sourced with
++. your/sdk/path/environment-setup+ to export a number of environment
+variables that will help cross-compile your projects using the
+Buildroot SDK: the +PATH+ will contain the SDK binaries, standard
+_autotools_ variables will be defined with the appropriate values, and
++CONFIGURE_FLAGS+ will contain basic +./configure+ options to
+cross-compile _autotools_ projects. It also provides some useful
+commands. Note however that once this script is sourced, the
+environment is setup only for cross-compilation, and no longer for
+native compilation.