github: Run test-ffmpeg on all 4 architectures

Test both i686 and x86_64, and armv7 and aarch64 on windows-11-arm
runners.

Building this on arm requires passing the --host option; on x86
the default "uname -m" works for both i686 and x86_64 (ffmpeg's
configure maps this to the architecture "x86", and the pointer
size is tested from the compiler), but for arm architectures we
need to specify them explicitly.

Author: jeremyd2019

.github/workflows/build.yml

@@ -750,7 +750,15 @@ jobs:
   test-ffmpeg:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
     needs: [linux-cross-windows]
-    runs-on: windows-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        arch:
+          - i686
+          - x86_64
+          - armv7
+          - aarch64
+    runs-on: ${{startsWith(matrix.arch, 'a') && 'windows-11-arm' || 'windows-latest'}}
     defaults:
       run:
         shell: msys2 {0}
@@ -771,7 +779,7 @@ jobs:
             nasm:p
       - uses: actions/download-artifact@v4
         with:
-          name: windows-ucrt-x86_64-toolchain
+          name: windows-ucrt-${{matrix.arch}}-toolchain
       - name: Unpack toolchain
         run: |
           unzip -q llvm-mingw-*.zip
@@ -789,7 +797,7 @@ jobs:
           export PATH=/llvm-mingw/bin:$PATH
           mkdir ffmpeg-build
           cd ffmpeg-build
-          ../ffmpeg/configure --samples=../fate-samples --enable-gpl
+          ../ffmpeg/configure --arch=${{matrix.arch}} --samples=../fate-samples --enable-gpl
           make -j$(nproc)
           make fate-rsync
           make -j$(nproc) fate