CI: Add MinGW/GCC build to Windows GHA

.github/workflows/windows_builds.yml

@@ -30,7 +30,7 @@ jobs:
             # Skip debug symbols, they're way too big with MSVC.
             sconsflags: debug_symbols=no vsproj=yes vsproj_gen_only=no windows_subsystem=console
             bin: ./bin/godot.windows.editor.x86_64.exe
-            artifact: true
+            compiler: msvc
 
           - name: Editor w/ clang-cl (target=editor, tests=yes, use_llvm=yes)
             cache-name: windows-editor-clang
@@ -38,6 +38,7 @@ jobs:
             tests: true
             sconsflags: debug_symbols=no windows_subsystem=console use_llvm=yes
             bin: ./bin/godot.windows.editor.x86_64.llvm.exe
+            compiler: clang
 
           - name: Template (target=template_release, tests=yes)
             cache-name: windows-template
@@ -45,7 +46,16 @@ jobs:
             tests: true
             sconsflags: debug_symbols=no
             bin: ./bin/godot.windows.template_release.x86_64.console.exe
-            artifact: true
+            compiler: msvc
+
+          - name: Template w/ GCC (target=template_release, tests=yes, use_mingw=yes)
+            cache-name: windows-template-gcc
+            # MinGW takes MUCH longer to compile; save time by only targeting Template.
+            target: template_release
+            tests: true
+            sconsflags: debug_symbols=no use_mingw=yes
+            bin: ./bin/godot.windows.template_release.x86_64.console.exe
+            compiler: gcc
 
     steps:
       - name: Checkout
@@ -69,16 +79,21 @@ jobs:
         uses: dsaltares/fetch-gh-release-asset@1.1.2
         with:
           repo: godotengine/godot-angle-static
-          version: tags/chromium/6029
-          file: Windows.6029-1.MSVC_17.x86_64.x86_32.zip
+          version: tags/chromium/6601.2
+          file: godot-angle-static-x86_64-${{ matrix.compiler == 'gcc' && 'gcc' || 'msvc' }}-release.zip
           target: angle/angle.zip
 
       - name: Extract pre-built ANGLE static libraries
         run: Expand-Archive -Force angle/angle.zip ${{ github.workspace }}/
 
       - name: Setup MSVC problem matcher
+        if: matrix.compiler == 'msvc'
         uses: ammaraskar/msvc-problem-matcher@master
 
+      - name: Setup GCC problem matcher
+        if: matrix.compiler != 'msvc'
+        uses: ammaraskar/gcc-problem-matcher@master
+
       - name: Compilation
         uses: ./.github/actions/godot-build
         with:
@@ -94,12 +109,12 @@ jobs:
         continue-on-error: true
 
       - name: Prepare artifact
-        if: ${{ matrix.artifact }}
+        if: matrix.compiler == 'msvc'
         run: |
           Remove-Item bin/* -Include *.exp,*.lib,*.pdb -Force
 
       - name: Upload artifact
-        if: ${{ matrix.artifact }}
+        if: matrix.compiler == 'msvc'
         uses: ./.github/actions/upload-artifact
         with:
           name: ${{ matrix.cache-name }}