ci: Implement MXE CI/CD build job

.ci/mxe.sh

@@ -0,0 +1,26 @@
+#!/bin/bash -ex
+
+# TODO: Why doesn't the CI environment use the PATH set in the Dockerimage?
+#       It works fine when using the image locally.
+export PATH="/mxe/usr/bin:${PATH}"
+
+mkdir build && cd build
+
+if [ "$GITHUB_REF_TYPE" == "tag" ]; then
+	export EXTRA_CMAKE_FLAGS=(-DENABLE_QT_UPDATE_CHECKER=ON)
+fi
+
+x86_64-w64-mingw32.shared-cmake .. \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DCMAKE_C_COMPILER_LAUNCHER=ccache \
+    -DCMAKE_CXX_COMPILER_LAUNCHER=ccache \
+    -DENABLE_QT_TRANSLATION=ON \
+    -DUSE_DISCORD_PRESENCE=ON \
+    -DUSE_SYSTEM_BOOST=ON \
+    -DUSE_SYSTEM_CRYPTOPP=ON \
+	"${EXTRA_CMAKE_FLAGS[@]}"
+x86_64-w64-mingw32.shared-cmake --build . -- -j$(nproc)
+x86_64-w64-mingw32.shared-strip -s bin/Release/*.exe
+make bundle
+
+ccache -s -v

.ci/pack.sh

@@ -36,10 +36,10 @@ function pack_artifacts() {
     fi
 
     # Create .zip/.tar.gz
-    if [ "$OS" = "windows" ]; then
+    if [ "$OS" = "windows" ] && [ "$TARGET" != "mxe" ]; then
         ARCHIVE_FULL_NAME="$ARCHIVE_NAME.zip"
         powershell Compress-Archive "$REV_NAME" "$ARCHIVE_FULL_NAME"
-    elif [ "$OS" = "android" ] || [ "$OS" = "macos" ]; then
+    elif [ "$OS" = "android" ] || [ "$OS" = "macos" ] || [ "$TARGET" = "mxe" ]; then
         ARCHIVE_FULL_NAME="$ARCHIVE_NAME.zip"
         zip -r "$ARCHIVE_FULL_NAME" "$REV_NAME"
     else

.github/workflows/build.yml

@@ -143,11 +143,21 @@ jobs:
           path: artifacts/
 
   windows:
-    runs-on: windows-latest
     strategy:
       fail-fast: false
       matrix:
-        target: ["msvc", "msys2"]
+        include:
+        - target: msvc
+          os: windows-latest
+        - target: msys2
+          os: windows-latest
+        - target: mxe
+          os: ubuntu-latest
+          container:
+            image: opensauce04/azahar-build-environment:latest
+            options: -u 1001
+    runs-on: ${{ matrix.os }}
+    container: ${{ matrix.container }}
     defaults:
       run:
         shell: ${{ (matrix.target == 'msys2' && 'msys2') || 'bash' }} {0}
@@ -195,23 +205,35 @@ jobs:
         with:
           args: install ptime wget
       - name: Install NSIS
-        if: ${{ github.ref_type == 'tag' }}
+        if: ${{ github.ref_type == 'tag' && matrix.target != 'mxe' }}
         run: |
           wget https://download.sourceforge.net/project/nsis/NSIS%203/3.11/nsis-3.11-setup.exe -O D:/a/_temp/nsis-setup.exe
           ptime D:/a/_temp/nsis-setup.exe /S
         shell: pwsh
       - name: Disable line ending translation
         run: git config --global core.autocrlf input
-      - name: Build
+      - name: Build (Native)
+        if: ${{ matrix.target != 'mxe' }}
         run: ./.ci/windows.sh
-      - name: Generate installer
-        if: ${{ github.ref_type == 'tag' }}
+      - name: Build (MXE)
+        if: ${{ matrix.target == 'mxe' }}
+        run: ./.ci/mxe.sh
+      - name: Generate installer (Native)
+        if: ${{ github.ref_type == 'tag' && matrix.target != 'mxe' }}
         run: |
           cd src\installer
           "C:\Program Files (x86)\NSIS\makensis.exe" /DPRODUCT_VARIANT=${{ matrix.target }} /DPRODUCT_VERSION=${{ github.ref_name }} citra.nsi
           mkdir ..\..\artifacts 2> NUL
           move /y *.exe ..\..\artifacts\
         shell: cmd
+      - name: Generate installer (MXE)
+        if: ${{ github.ref_type == 'tag' && matrix.target == 'mxe' }}
+        run: |
+          export PATH="/mxe/usr/bin:${PATH}" # TODO: Why do we have to do this if it's in the image?
+          cd src/installer
+          x86_64-w64-mingw32.shared-makensis -DPRODUCT_VARIANT=${{ matrix.target }} -DPRODUCT_VERSION=${{ github.ref_name }} citra.nsi
+          mkdir -p ../../artifacts
+          mv ./*.exe ../../artifacts/
       - name: Pack
         run: ./.ci/pack.sh
       - name: Upload