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/support/gnuconfig/README.buildroot

@@ -13,15 +13,9 @@ files of your package to be updated by using:
 <pkg>_POST_PATCH_HOOKS += UPDATE_CONFIG_HOOK
 
 --- UPDATE ---
-GNU config is now managed in git, so to update:
+Run the script 'update' in this directory, and commit the result.
 
-# git clone git://git.savannah.gnu.org/config.git
-# cp config/config.* .
-# for p in $(ls patches/*.patch); do patch -p1 < $p; done
-# rm -rf config
+The current Buildroot version is based on this commit of the config.git
+repository (leave alone on its own line, the script updates it):
 
-Currently no patches are needed, but they may be needed again in the
-future.
-
-The current Buildroot version is based on the Git commit
-104ee6463c4bfaac3f3029d9be9bdd6e93879323 of the config.git repository.
+d7a4dee7cc25e332b990d0a6d9f0ddd42cb33cf5