Windows: flip default to Ninja, add MSVC classifier, add GPU classifiers

.github/build.bat

@@ -38,15 +38,28 @@ if /I "%USE_CACHE%"=="true" (
     )
 )
 
+REM NOTE: nvcc is NOT wrapped with sccache on Windows. Unlike build.sh (Linux) -- where
+REM sccache caches the per-arch .cu device passes -- sccache on Windows cannot parse the
+REM nvcc command line (it dies with `sccache: error: Could not parse shell line` and
+REM fails every .cu compile). So CUDA device code is built by nvcc directly (uncached)
+REM here; the cl.exe C/C++ TUs still cache via the C/CXX launcher set above.
+
 mkdir build
 cmake -Bbuild %LAUNCH% %*
-if errorlevel 1 exit /b %ERRORLEVEL%
+if errorlevel 1 exit /b 1
 cmake --build build --config Release
-if errorlevel 1 exit /b %ERRORLEVEL%
+set "BUILD_RC=!ERRORLEVEL!"
 
-REM Only query stats when sccache was actually wired in as the launcher; re-invoking
-REM a rejected/crashing sccache here would just repeat its failure output.
+REM Print cache stats (best-effort) regardless of build outcome -- only when sccache
+REM was wired in as the launcher.
 if defined LAUNCH (
     echo build.bat: sccache --show-stats
     sccache --show-stats
 )
+
+REM Propagate a build failure as a non-zero exit (a prior bug let a failed `cmake
+REM --build` reach here and exit 0, masquerading as a green build with no artifacts).
+if not "!BUILD_RC!"=="0" (
+    echo build.bat: cmake --build failed with exit code !BUILD_RC!.
+    exit /b !BUILD_RC!
+)

.github/build_opencl_android.sh

@@ -20,9 +20,9 @@ HEADERS_DIR="$OPENCL_STAGE/OpenCL-Headers"
 LOADER_DIR="$OPENCL_STAGE/OpenCL-ICD-Loader"
 LOADER_BUILD="$LOADER_DIR/build"
 
-# Pinned tags for reproducibility.
-HEADERS_TAG=v2025.07.22
-LOADER_TAG=v2025.07.22
+# Pinned tags for reproducibility (OpenCL 3.1.1 spec release).
+HEADERS_TAG=v2026.05.29
+LOADER_TAG=v2026.05.29
 
 if [ ! -d "$HEADERS_DIR" ]; then
     mkdir -p "$OPENCL_STAGE"

.github/build_opencl_windows.bat

@@ -0,0 +1,54 @@
+REM SPDX-FileCopyrightText: 2026 Bernard Ladenthin <bernard.ladenthin@gmail.com>
+REM
+REM SPDX-License-Identifier: MIT
+REM
+REM Windows x86_64 build with the OpenCL backend enabled, shipped as the
+REM `opencl-windows-x86-64` classifier. The windows-2025 runner image ships
+REM neither OpenCL headers nor an OpenCL import library, so this script first
+REM stages Khronos OpenCL-Headers and builds OpenCL-ICD-Loader (producing
+REM OpenCL.lib) before delegating the jllama configure+build to build.bat with
+REM the OpenCL paths. Mirrors build_opencl_android.sh.
+REM
+REM At runtime the GPU vendor's ICD (System32\OpenCL.dll, installed by the
+REM NVIDIA/AMD/Intel driver) provides the actual OpenCL symbols; we link only
+REM against the loader's import library, so no OpenCL.dll is shipped.
+
+@echo off
+setlocal enabledelayedexpansion
+
+set "OPENCL_STAGE=%RUNNER_TEMP%\opencl-stage"
+if "%RUNNER_TEMP%"=="" set "OPENCL_STAGE=%TEMP%\opencl-stage"
+set "HEADERS_DIR=%OPENCL_STAGE%\OpenCL-Headers"
+set "LOADER_DIR=%OPENCL_STAGE%\OpenCL-ICD-Loader"
+set "LOADER_BUILD=%LOADER_DIR%\build"
+
+REM Pinned tags for reproducibility (OpenCL 3.1.1; match build_opencl_android.sh).
+set "HEADERS_TAG=v2026.05.29"
+set "LOADER_TAG=v2026.05.29"
+
+if not exist "%HEADERS_DIR%" (
+    git clone --depth 1 --branch %HEADERS_TAG% https://github.com/KhronosGroup/OpenCL-Headers.git "%HEADERS_DIR%"
+    if errorlevel 1 exit /b 1
+)
+
+if not exist "%LOADER_BUILD%\Release\OpenCL.lib" if not exist "%LOADER_BUILD%\OpenCL.lib" (
+    if not exist "%LOADER_DIR%" (
+        git clone --depth 1 --branch %LOADER_TAG% https://github.com/KhronosGroup/OpenCL-ICD-Loader.git "%LOADER_DIR%"
+        if errorlevel 1 exit /b 1
+    )
+    cmake -B "%LOADER_BUILD%" -S "%LOADER_DIR%" -DOPENCL_ICD_LOADER_HEADERS_DIR="%HEADERS_DIR%" -DBUILD_TESTING=OFF
+    if errorlevel 1 exit /b 1
+    cmake --build "%LOADER_BUILD%" --config Release
+    if errorlevel 1 exit /b 1
+)
+
+REM Resolve the import library: multi-config generators emit build\Release\OpenCL.lib,
+REM single-config ones emit build\OpenCL.lib.
+set "OPENCL_LIB=%LOADER_BUILD%\Release\OpenCL.lib"
+if not exist "%OPENCL_LIB%" set "OPENCL_LIB=%LOADER_BUILD%\OpenCL.lib"
+
+REM Delegate to build.bat so the jllama build inherits the sccache probe + Depot
+REM cache launcher and --show-stats output. The OpenCL paths satisfy ggml's
+REM find_package(OpenCL); the caller appends -G/-DGGML_OPENCL/-DOS_* via %*.
+call .github\build.bat -DOpenCL_INCLUDE_DIR="%HEADERS_DIR%" -DOpenCL_LIBRARY="%OPENCL_LIB%" %*
+exit /b %ERRORLEVEL%