Add "smoke test" examples compilation CI workflow

On every push or pull request that affects platform source code or bundled libraries, compile example
sketches of all bundled libraries for the platform's boards.

.github/workflows/compile-platform-examples.yml

+name: Compile Examples
+
+# See: https://docs.github.com/en/actions/reference/events-that-trigger-workflows
+on:
+  push:
+    paths:
+      - ".github/workflows/compile-platform-examples.ya?ml"
+      - "cores/**"
+      - "libraries/**"
+      - "variants/**"
+      - "boards.txt"
+      - "platform.txt"
+  pull_request:
+    paths:
+      - ".github/workflows/compile-platform-examples.ya?ml"
+      - "cores/**"
+      - "libraries/**"
+      - "variants/**"
+      - "boards.txt"
+      - "platform.txt"
+  workflow_dispatch:
+  repository_dispatch:
+
+jobs:
+  build:
+    name: ${{ matrix.board.fqbn }}
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+
+      matrix:
+        board:
+          - fqbn: arduino:avr:yun
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:uno
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:diecimila:cpu=atmega328
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:diecimila:cpu=atmega168
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:nano:cpu=atmega328
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:nano:cpu=atmega328old
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:nano:cpu=atmega168
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:mega:cpu=atmega2560
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:mega:cpu=atmega1280
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:megaADK
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:leonardo
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:leonardoeth
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:micro
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:esplora
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:mini:cpu=atmega328
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:mini:cpu=atmega168
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:ethernet
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:fio
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:bt:cpu=atmega328
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:bt:cpu=atmega168
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:LilyPadUSB
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:lilypad:cpu=atmega328
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:lilypad:cpu=atmega168
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:pro:cpu=16MHzatmega328
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:pro:cpu=8MHzatmega328
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:pro:cpu=16MHzatmega168
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:pro:cpu=8MHzatmega168
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:atmegang:cpu=atmega168
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:atmegang:cpu=atmega8
+            serial: true
+            softwareserial: false
+          - fqbn: arduino:avr:robotControl
+            serial: true
+            softwareserial: false
+          - fqbn: arduino:avr:robotMotor
+            serial: true
+            softwareserial: false
+          - fqbn: arduino:avr:gemma
+            serial: false
+            softwareserial: false
+          - fqbn: arduino:avr:circuitplay32u4cat
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:yunmini
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:chiwawa
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:one
+            serial: true
+            softwareserial: true
+          - fqbn: arduino:avr:unowifi
+            serial: true
+            softwareserial: true
+
+        # Make board type-specific customizations to the matrix jobs
+        include:
+          - board:
+              # Boards with Serial interface
+              serial: true
+            # Compile these sketches in addition to the ones compiled for all boards
+            serial-sketch-paths: |
+              - libraries/EEPROM/examples/eeprom_crc
+              - libraries/EEPROM/examples/eeprom_get
+              - libraries/EEPROM/examples/eeprom_put
+              - libraries/EEPROM/examples/eeprom_read
+              - libraries/SPI
+              - libraries/Wire
+          - board:
+              serial: false
+            serial-sketch-paths: ""
+          - board:
+              # Boards compatible with the SoftwareSerial library
+              softwareserial: true
+            softwareserial-sketch-paths: |
+              - libraries/SoftwareSerial
+          - board:
+              softwareserial: false
+            softwareserial-sketch-paths: ""
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Compile examples
+        uses: arduino/compile-sketches@v1
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          fqbn: ${{ matrix.board.fqbn }}
+          platforms: |
+            # Use Boards Manager to install the latest release of the platform to get the toolchain.
+            - name: arduino:avr
+            # Overwrite the Boards Manager installation with the platform from the repository.
+            - source-path: ./
+              name: arduino:avr
+          sketch-paths: |
+            - libraries
+            # Compile these sketches for all boards
+            - libraries/EEPROM/examples/eeprom_clear
+            - libraries/EEPROM/examples/eeprom_iteration
+            - libraries/EEPROM/examples/eeprom_update
+            - libraries/EEPROM/examples/eeprom_write
+            # Board-specific sketches
+            ${{ matrix.serial-sketch-paths }}
+            ${{ matrix.softwareserial-sketch-paths }}

README.md

 # Arduino AVR Boards
 
 [![Check Arduino status](https://github.com/arduino/ArduinoCore-avr/actions/workflows/check-arduino.yml/badge.svg)](https://github.com/arduino/ArduinoCore-avr/actions/workflows/check-arduino.yml)
+[![Compile Examples status](https://github.com/arduino/ArduinoCore-avr/actions/workflows/compile-platform-examples.yml/badge.svg)](https://github.com/arduino/ArduinoCore-avr/actions/workflows/compile-platform-examples.yml)
 [![Spell Check status](https://github.com/arduino/ArduinoCore-avr/actions/workflows/spell-check.yml/badge.svg)](https://github.com/arduino/ArduinoCore-avr/actions/workflows/spell-check.yml)
 
 This repository contains the source code and configuration files of the Arduino AVR Boards