CI: tentatively enable LLVM through vcpkg

Author: Hugobros3

.github/workflows/cmake-multi-platform.yml

@@ -89,10 +89,10 @@ jobs:
       run: |
         echo "CMAKE_PLATFORM_SPECIFIC_ARGS=${{ env.CMAKE_PLATFORM_SPECIFIC_ARGS }} -DLLVM_DIR=/usr/lib/llvm-14/cmake" >> $GITHUB_ENV
 
-    - name: Install json-c (vcpkg)
+    - name: Install json-c, LLVM and Clang (vcpkg)
       if: startsWith(matrix.os,'windows')
       run: |
-        vcpkg install json-c
+        vcpkg install json-c llvm llvm[clang]
         echo "CMAKE_PLATFORM_SPECIFIC_ARGS=-DCMAKE_TOOLCHAIN_FILE=C:/vcpkg/scripts/buildsystems/vcpkg.cmake" >> "$env:GITHUB_ENV"
 
     - name: Configure CMake