CI: Add workflow to test Meson and CMake builds

This adds a workflow using GitHub Actions which builds libwpe twice: one
time with CMake, and another with Meson. Both results are checked to
ensure that both build systems produce the same set of headers (and with
the same contents), and libraries with the same public symbols.

Author: aperezdc

.github/workflows/ci.yml

@@ -0,0 +1,71 @@
+---
+
+name: CI
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-16.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Install Debian Packages
+        run: |
+          sudo apt update
+          sudo apt install -y cmake flex libjson-glib-dev libxkbcommon-dev \
+            libegl1-mesa-dev libxml2-dev libxslt1-dev libyaml-dev llvm-dev \
+            libclang-dev libglib2.0-dev ninja-build
+      - name: Setup Python
+        uses: actions/setup-python@v1
+        with:
+          python-version: 3.6
+      - name: Python Package Cache
+        uses: actions/cache@v1
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ hashFiles('.github/workflows/ci.yml') }}
+          restore-keys: ${{ runner.os }}-pip-
+      - name: Install Python Packages
+        run: |
+          python -m pip install --upgrade pip setuptools wheel
+          HOTDOC_BUILD_C_EXTENSION=enabled pip install hotdoc meson
+      - name: Meson - Configure
+        run: |
+          mkdir -p _work/meson
+          meson _work/meson/build --prefix /usr -Dbuild-docs=true
+      - name: Meson - Build
+        run: |
+          ninja -C _work/meson/build
+      - name: Meson - Install
+        run: |
+          DESTDIR="$(pwd)/_work/meson/prefix" ninja -C _work/meson/build install
+          nm -D _work/meson/build/libwpe-1.0.so | sort -u > _work/meson/symbols
+          (cd _work/meson/prefix && find lib -type f | sort) > _work/meson/files
+      - name: Meson - Archive Artifacts
+        uses: actions/upload-artifact@v1
+        with:
+          name: build-meson
+          path: _work/meson/prefix
+      - name: CMake - Configure
+        run: |
+          mkdir -p _work/cmake/build && cd $_
+          cmake -DCMAKE_INSTALL_PREFIX=/usr -DBUILD_DOCS=ON ../../..
+      - name: CMake - Build
+        run: |
+          make -C _work/cmake/build -j$(nproc)
+      - name: CMake - Install
+        run: |
+          DESTDIR="$(pwd)/_work/cmake/prefix" make -C _work/cmake/build install
+          nm -D _work/cmake/build/libwpe-1.0.so | sort -u > _work/cmake/symbols
+          (cd _work/cmake/prefix && find lib -type f | sort) > _work/cmake/files
+      - name: CMake - Archive Artifacts
+        uses: actions/upload-artifact@v1
+        with:
+          name: build-cmake
+          path: _work/cmake/prefix
+      - name: Check Installations
+        run: |
+          diff -u _work/{cmake,meson}/files
+          diff -u _work/{cmake,meson}/symbols
+          diff -Naur _work/{cmake,meson}/prefix/usr/include/