CI: add Kernel compile tests

Add Github Actions yaml script to build test kernel PR changes for
each target.

Signed-off-by: Paul Spooren <mail@aparcar.org>
[ add commit description ]
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

.github/workflows/kernel.yml

@@ -0,0 +1,143 @@
+name: Build Kernel
+
+on:
+  pull_request:
+    paths:
+      - 'include/kernel-*'
+      - 'package/kernel/**'
+jobs:
+  determine_targets:
+    name: Set targets
+    runs-on: ubuntu-latest
+    outputs:
+      target: ${{ steps.find_targets.outputs.target }}
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Set targets
+        id: find_targets
+        run: |
+          export TARGETS="$(perl ./scripts/dump-target-info.pl targets 2>/dev/null \
+            | sort -u -t '/' -k1,1 \
+            | awk '{ print $1 }')"
+
+          JSON='['
+          FIRST=1
+          for TARGET in $TARGETS; do
+            [[ $FIRST -ne 1 ]] && JSON="$JSON"','
+            JSON="$JSON"'"'"${TARGET}"'"'
+            FIRST=0
+          done
+          JSON="$JSON"']'
+
+           echo -e "\n---- targets ----\n"
+           echo "$JSON"
+           echo -e "\n---- targets ----\n"
+
+           echo "::set-output name=target::$JSON"
+
+  build:
+    name: Build Kernel with external toolchain
+    needs: determine_targets
+    runs-on: ubuntu-latest
+    strategy:
+       fail-fast: False
+       matrix:
+         target: ${{fromJson(needs.determine_targets.outputs.target)}}
+
+    steps:
+      - name: Checkout master directory
+        uses: actions/checkout@v2
+        with:
+          path: openwrt
+
+      - name: Setup Ubuntu
+        env:
+          DEBIAN_FRONTEND: noninteractive
+        run: |
+          sudo apt-get update
+          sudo apt-get -y install \
+            build-essential \
+            ccache \
+            clang-12 \
+            ecj \
+            fastjar \
+            file \
+            g++ \
+            gawk \
+            gettext \
+            git \
+            java-propose-classpath \
+            libelf-dev \
+            libncurses-dev \
+            libssl-dev \
+            mkisofs \
+            python3 \
+            python3-dev \
+            python3-distutils \
+            python3-setuptools \
+            qemu-utils \
+            rsync \
+            subversion \
+            swig \
+            unzip \
+            wget \
+            xsltproc \
+            zlib1g-dev
+
+      - name: Initialization environment
+        run: |
+          TARGET=$(echo ${{ matrix.target }} | cut -d "/" -f 1)
+          SUBTARGET=$(echo ${{ matrix.target }} | cut -d "/" -f 2)
+          echo "TARGET=$TARGET" >> "$GITHUB_ENV"
+          echo "SUBTARGET=$SUBTARGET" >> "$GITHUB_ENV"
+
+      - name: Update & Install feeds
+        run: |
+          cd openwrt
+          ./scripts/feeds update -a
+          ./scripts/feeds install -a
+
+      - name: Setup external toolchain
+        run: |
+          cd openwrt
+          TOOLCHAIN_FILE=$(curl "https://downloads.openwrt.org/snapshots/targets/${{ env.TARGET }}/${{ env.SUBTARGET }}/sha256sums" \
+            | sed -n -e 's/.*\(openwrt-toolchain.*\).tar.xz/\1/p')
+
+          echo "TOOLCHAIN_FILE=$TOOLCHAIN_FILE" >> "$GITHUB_ENV"
+          
+          wget -O - https://downloads.openwrt.org/snapshots/targets/${{ env.TARGET }}/${{ env.SUBTARGET }}/${TOOLCHAIN_FILE}.tar.xz \
+            | tar --xz -xf -
+
+      - name: Configure external toolchain
+        run: |
+          cd openwrt
+          ./scripts/ext-toolchain.sh \
+            --toolchain ${{ env.TOOLCHAIN_FILE }}/toolchain-* \
+            --config ${{ env.TARGET }}/${{ env.SUBTARGET }}
+
+          make defconfig
+
+      - name: Build tools
+        run: |
+          cd openwrt
+          make tools/install -j$(nproc) BUILD_LOG=1
+
+      - name: Build toolchain
+        run: |
+          cd openwrt
+          make toolchain/install -j$(nproc) BUILD_LOG=1
+
+      - name: Build Kernel
+        run: |
+          cd openwrt
+          make target/compile -j$(nproc) BUILD_LOG=1
+
+      - name: Upload logs
+        if: failure()
+        uses: actions/upload-artifact@v2
+        with:
+          name: ${{ env.TARGET }}-${{ env.SUBTARGET }}-logs
+          path: "openwrt/logs"