Add experimental CI using Kas+GitLab

Add kas scripts that generic to test builds, and a GitLab CI runner.

This is mainly a cut-down copy of what is in the master/gatesgarth
branches with the following changes:

- Just the BSPs that are in the Dunfell release, obviously
- No clang testing. There are patches in master that can be backported
  if required.
- Added testing of the armgcc-9.2 compiler. This is currently broken for
  some configurations in master and the testing will be forward-ported
  when it passes.

Change-Id: I9c2a4f66318b3ccc066d423f3533202ee33f0c9d
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

.gitlab-ci.yml

@@ -0,0 +1,105 @@
+# Use our custom Crops-derived image
+image: $CI_REGISTRY/$CI_PROJECT_NAMESPACE/yocto-builder:master
+
+  # First do a common bootstrap, and then build all the targets
+stages:
+  - bootstrap
+  - build
+
+# Common job fragment to get a worker ready
+.setup:
+  # Retry because the runner is flakey (see https://gitlab.com/gitlab-org/gitlab-runner/-/issues/2890)
+  retry: 2
+  stage: build
+  variables:
+    KAS_WORK_DIR: $CI_PROJECT_DIR/work
+    SSTATE_DIR: $CI_BUILDS_DIR/persist/sstate
+    DL_DIR: $CI_BUILDS_DIR/persist/downloads
+  before_script:
+    - echo KAS_WORK_DIR = $KAS_WORK_DIR
+    - echo SSTATE_DIR = $SSTATE_DIR
+    - echo DL_DIR = $DL_DIR
+    - mkdir --verbose --parents $KAS_WORK_DIR $SSTATE_DIR $DL_DIR
+
+# Generalised fragment to do a Kas build
+.build:
+  extends: .setup
+  script:
+  - KASFILES=$(kas/jobs-to-kas $CI_JOB_NAME)
+  - kas shell --update --force-checkout $KASFILES -c 'cat conf/*.conf'
+  - kas build $KASFILES
+
+
+#
+# First phase, bootstrap and machine coverage
+#
+
+# Build a number of native tools first to ensure the other builders don't race
+# over them
+bootstrap:
+  extends: .build
+  stage: bootstrap
+  variables:
+    KAS_TARGET: binutils-cross-aarch64 gcc-cross-aarch64 python3-native opkg-native rpm-native
+  script:
+  - kas build kas/n1sdp.yml
+
+# What percentage of machines in the layer do we build
+machine-coverage:
+  stage: bootstrap
+  script:
+  - ./kas/check-machine-coverage
+  coverage: '/Coverage: \d+/'
+
+
+#
+# Second phase, the actual build jobs
+#
+
+a5ds:
+  extends: .build
+
+foundation-armv8:
+  extends: .build
+
+fvp-base:
+  extends: .build
+
+gem5-arm64:
+  extends: .build
+
+juno:
+  extends: .build
+
+juno/musl:
+  extends: .build
+
+n1sdp:
+  extends: .build
+
+n1sdp/armgcc:
+  extends: .build
+
+tc0:
+  extends: .build
+
+
+#
+# Utility tasks, not executed automatically
+#
+
+# Report on disk usage
+usage:
+  extends: .setup
+  stage: bootstrap
+  when: manual
+  script:
+  - du -h -s $DL_DIR $SSTATE_DIR
+
+# Wipe out old sstate
+prune-sstate:
+  extends: .setup
+  stage: bootstrap
+  when: manual
+  script:
+  - find $SSTATE_DIR -type f -atime +30 -delete