GHA CI: Backport latest changes (#15361)

By having unified github workflows, the building cache would be utilized
more efficiently as the total cache size will be smaller (no more vcpkg
caching on macOS CI) and will stop thrashing the build cache (large
vcpkg cache evicts other smaller cache).

Relevant PRs:
#15321
#15340
#15342
#15355

.github/workflows/ci_macos.yaml

@@ -0,0 +1,73 @@
+name: CI - macOS
+on: [pull_request, push]
+
+jobs:
+  ci:
+    name: Build
+    runs-on: macos-10.15
+
+    strategy:
+      matrix:
+        libt_version: ["v1.2.12"]
+        qbt_gui: ["GUI=ON", "GUI=OFF"]
+      fail-fast: false
+
+    env:
+      openssl_root: /usr/local/opt/openssl@1.1
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Setup ccache
+        uses: hendrikmuhs/ccache-action@v1
+        with:
+          key: ${{ runner.os }}
+
+      - name: Install dependencies
+        run: |
+          brew update > /dev/null
+          brew install \
+            cmake ninja \
+            boost openssl@1.1 qt@5 zlib
+          brew link --force \
+            qt@5
+          # workaround for cmake + Qt
+          sudo ln -s /usr/local/opt/qt@5/mkspecs /usr/local/mkspecs
+          sudo ln -s /usr/local/opt/qt@5/plugins /usr/local/plugins
+
+      - name: Install libtorrent
+        run: |
+          git clone --branch ${{ matrix.libt_version }} --depth 1 https://github.com/arvidn/libtorrent.git
+          cd libtorrent
+          git submodule update --init --recursive
+          export PATH="/usr/lib/ccache:/usr/local/opt/ccache/libexec:$PATH"
+          cmake \
+            -B build \
+            -G "Ninja" \
+            -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+            -DCMAKE_CXX_STANDARD=17 \
+            -Ddeprecated-functions=OFF \
+            -DOPENSSL_ROOT_DIR="${{ env.openssl_root }}"
+          cmake --build build
+          sudo cmake --install build
+
+      - name: Build qBittorrent
+        run: |
+          export PATH="/usr/lib/ccache:/usr/local/opt/ccache/libexec:$PATH"
+          cmake \
+            -B build \
+            -G "Ninja" \
+            -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+            -D${{ matrix.qbt_gui }} \
+            -DVERBOSE_CONFIGURE=ON \
+            -DOPENSSL_ROOT_DIR="${{ env.openssl_root }}"
+          cmake --build build
+
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v2
+        with:
+          name: qBittorrent-CI_macOS_${{ matrix.qbt_gui }}_libtorrent-${{ matrix.libt_version }}
+          path: |
+            build/qbittorrent.app
+            build/qbittorrent-nox.app