ci: Add CMake+Ninja+Clang to the AppVeyor CI matrix
diff --git a/.appveyor.yml b/.appveyor.yml
index af232d9..b850d02 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -21,6 +21,9 @@
       AUTOMATION: cmake
       ARCH: arm64
       CI_NO_TEST: 1
+    - TOOLCHAIN: llvm
+      AUTOMATION: cmake
+      ARCH: x64
     - TOOLCHAIN: msys2
       AUTOMATION: cmake
       ARCH: i686
@@ -43,6 +46,8 @@
 install:
   - 'if "%TOOLCHAIN%"=="vstudio" C:\tools\vcpkg\vcpkg.exe install zlib:%ARCH%-windows'
   - 'if "%TOOLCHAIN%"=="vstudio" C:\tools\vcpkg\vcpkg.exe integrate install'
+  - 'if "%TOOLCHAIN%"=="llvm" C:\tools\vcpkg\vcpkg.exe install zlib:%ARCH%-windows'
+  - 'if "%TOOLCHAIN%"=="llvm" C:\tools\vcpkg\vcpkg.exe integrate install'
 
 before_build:
   - 'if "%TOOLCHAIN%"=="vstudio" set CI_CMAKE_GENERATOR=Visual Studio 17 2022'
@@ -50,10 +55,13 @@
   - 'if "%TOOLCHAIN%"=="vstudio" if "%ARCH%"=="x86" set CI_CMAKE_GENERATOR_PLATFORM=Win32'
   - 'if "%TOOLCHAIN%"=="vstudio" if "%ARCH%"=="x64" set CI_CMAKE_GENERATOR_PLATFORM=x64'
   - 'if "%TOOLCHAIN%"=="vstudio" if "%ARCH%"=="arm64" set CI_CMAKE_GENERATOR_PLATFORM=ARM64'
+  - 'if "%TOOLCHAIN%"=="llvm" set CI_CMAKE_GENERATOR=Ninja'
+  - 'if "%TOOLCHAIN%"=="llvm" set CI_CMAKE_TOOLCHAIN_FILE=C:\tools\vcpkg\scripts\buildsystems\vcpkg.cmake'
+  - 'if "%TOOLCHAIN%"=="llvm" set CI_CC=clang.exe'
   - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="cmake" set CI_CMAKE_GENERATOR=Unix Makefiles'
   - 'if "%TOOLCHAIN%"=="msys2" if "%ARCH%"=="i686" set PATH=C:\msys64\mingw32\bin;%PATH%'
   - 'if "%TOOLCHAIN%"=="msys2" if "%ARCH%"=="x86_64" set PATH=C:\msys64\mingw64\bin;%PATH%'
-  - 'if "%TOOLCHAIN%"=="msys2" set CI_CC=%ARCH%-w64-mingw32-gcc'
+  - 'if "%TOOLCHAIN%"=="msys2" set CI_CC=%ARCH%-w64-mingw32-gcc.exe'
   - 'set CI_CMAKE_BUILD_FLAGS=--parallel 2'
   - 'set CI_CTEST_FLAGS=--parallel 2'
   - 'set CI_MAKE_FLAGS=-j2'
@@ -61,6 +69,7 @@
 
 build_script:
   - 'if "%TOOLCHAIN%"=="vstudio" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_cmake.sh"'
+  - 'if "%TOOLCHAIN%"=="llvm" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_cmake.sh"'
   - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="cmake" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_cmake.sh"'
   - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="configure" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_configure.sh"'
   - 'if "%TOOLCHAIN%"=="msys2" if "%AUTOMATION%"=="makefiles" C:\msys64\usr\bin\bash.exe -l "%APPVEYOR_BUILD_FOLDER%\ci\ci_verify_makefiles.sh"'