ci: Add IDF v4.2 to build tests

Also fixes build issues when default config carried over IDF releases --
always remove previous `sdkconfig` before a new build

.gitlab-ci.yml

@@ -72,6 +72,11 @@ build_with_idf_v4:
     - export EXTRA_CFLAGS=${PEDANTIC_CFLAGS} && export EXTRA_CXXFLAGS=${EXTRA_CFLAGS}
     # build other examples
     - $MQTT_PATH/ci/build_examples.sh
+    # rebuild with IDFv4.2
+    - $MQTT_PATH/ci/set_idf.sh release/v4.2
+    - cd $IDF_PATH && tools/idf_tools.py --non-interactive install && eval "$(tools/idf_tools.py --non-interactive export)"
+    - $MQTT_PATH/ci/set_mqtt.sh $CI_COMMIT_SHA
+    - $MQTT_PATH/ci/build_examples.sh
     # rebuild with IDFv4.1
     - $MQTT_PATH/ci/set_idf.sh release/v4.1
     - cd $IDF_PATH && tools/idf_tools.py --non-interactive install && eval "$(tools/idf_tools.py --non-interactive export)"

ci/build_examples.sh

@@ -16,7 +16,7 @@ for i in $examples; do
         make defconfig
         make -j 4
     else
-        rm -rf build
+        rm -rf build sdkconfig
         idf.py build
     fi;
 done

ci/set_idf.sh

@@ -13,7 +13,7 @@ cd $IDF_PATH
 # Cleans out the untracked files in the repo, so the next "git checkout" doesn't fail
 git clean -f
 git checkout $1
-# Removes the mqtt submodule, not the next submodule update doesn't fail
+# Removes the mqtt submodule, so the next submodule update doesn't fail
 rm -rf $IDF_PATH/components/mqtt/esp-mqtt
-./tools/ci/mirror-submodule-update.sh
+git submodule update --init --recursive