ci : use dynamic libopenblas.dll for window-blas (#3177)

* ci : use dynamic libopenblas.dll for window-blas

This commit updates the windows-blas job to use the dynamic (can load
different kernels depending of the CPU arch) libopenblas.dll instead of
the "static" openblas.dll that get installed by vcpgk.

The motivation for this change is that there have been reports of
performance drops in later version specifically related to blas. Please
see the links below for more details.

Resolves: https://github.com/ggml-org/whisper.cpp/issues/3166
Refs: https://github.com/ggml-org/whisper.cpp/issues/2666#issuecomment-2885978811

.github/workflows/build.yml

@@ -629,11 +629,14 @@ jobs:
         arch: [Win32, x64]
         blas: [ON]
         sdl2: [ON]
+        blasver: [0.3.29]
         include:
           - arch: Win32
             s2arc: x86
+            blasfile: x86
           - arch: x64
             s2arc: x64
+            blasfile: x64_64
           - sdl2: ON
             s2ver: 2.28.5
 
@@ -654,7 +657,8 @@ jobs:
       - name: Install OpenBLAS and pkgconfiglite
         if: matrix.blas == 'ON'
         run: |
-          vcpkg install --triplet=${{ matrix.s2arc }}-windows openblas
+          Invoke-WebRequest "https://github.com/OpenMathLib/OpenBLAS/releases/download/v${{matrix.blasver}}/OpenBLAS-${{matrix.blasver}}_${{matrix.blasfile}}.zip" -OutFile "OpenBLAS-${{matrix.blasver}}.zip"
+          Expand-Archive "OpenBLAS-${{matrix.blasver}}.zip" -DestinationPath "OpenBLAS-${{matrix.blasver}}"
           choco install pkgconfiglite
 
       - name: Fetch SDL2 and set SDL2_DIR
@@ -671,6 +675,8 @@ jobs:
           -DCMAKE_BUILD_TYPE=${{ matrix.build }}
           -DGGML_BLAS=${{ matrix.blas }}
           -DGGML_BLAS_VENDOR=OpenBLAS
+          -DBLAS_LIBRARIES="$env:GITHUB_WORKSPACE/OpenBLAS-${{matrix.blasver}}/lib/libopenblas.lib"
+          -DBLAS_INCLUDE_DIRS="$env:GITHUB_WORKSPACE/OpenBLAS-${{matrix.blasver}}/include"
           -DWHISPER_SDL2=${{ matrix.sdl2 }}
 
       - name: Build
@@ -680,17 +686,12 @@ jobs:
 
       - name: Copy openblas.dll
         if: matrix.blas == 'ON'
-        run: copy "C:/vcpkg/packages/openblas_${{ matrix.s2arc }}-windows/bin/openblas.dll" build/bin/${{ matrix.build }}
+        run: copy "$env:GITHUB_WORKSPACE/OpenBLAS-${{matrix.blasver}}/bin/libopenblas.dll" build/bin/${{ matrix.build }}
 
       - name: Copy SDL2.dll
         if: matrix.sdl2 == 'ON'
         run: copy "$env:SDL2_DIR/../lib/${{ matrix.s2arc }}/SDL2.dll" build/bin/${{ matrix.build }}
 
-      - name: Pack bin artifacts
-        shell: pwsh
-        run: |
-              Compress-Archive -Path "build/bin/${{ matrix.build }}" -DestinationPath "whisper-blas-bin-${{ matrix.arch }}.zip"
-
       - name: Upload binaries
         if: matrix.blas == 'ON' && matrix.sdl2 == 'ON' && ${{ (github.event_name == 'push' && github.ref == 'refs/heads/master') ||
                 github.event.inputs.create_release == 'true' ||
@@ -698,7 +699,7 @@ jobs:
         uses: actions/upload-artifact@v4
         with:
           name: whisper-blas-bin-${{ matrix.arch }}.zip
-          path: whisper-blas-bin-${{ matrix.arch }}.zip
+          path: "build/bin/${{ matrix.build }}/**"
 
   windows-cublas:
     if: ${{ github.event_name == 'push' || github.event_name == 'pull_request' ||