Upload builds on push, and test that PRs build, with GH Actions

.github/workflows/build-and-upload.yml

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+name: build and upload
+
+# Controls when the workflow will run
+on:
+  # Triggers the workflow on push or pull request events but only for the main branch
+  push:
+    branches: [ master ]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  build:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      # Use embedded toolchain
+      - uses: numworks/setup-arm-toolchain@2020-q4
+
+      # Runs a single command using the runners shell
+      - name: Build
+        run: make
+
+      - name: Archive firmware build artifacts as a zip
+        uses: actions/upload-artifact@v2.2.4
+        with:
+          name: blackmagic-firmware.zip
+          path: src/blackmagic*
+          if-no-files-found: error

.github/workflows/build-pr.yml

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+name: build PR
+
+# Controls when the workflow will run
+on:
+  # Triggers the workflow on push or pull request events but only for the main branch
+  pull_request:
+    branches: [ master ]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  build:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      # Use embedded toolchain
+      - uses: numworks/setup-arm-toolchain@2020-q4
+
+      # Runs a single command using the runners shell
+      - name: Build
+        run: make