Switch Windows build configuration to use LLVM and GCC tooling

Replaced MSVC with LLVM (v17.0) as the compiler and updated the build environment to use GCC for ccache. Simplified configuration by removing MSVC-specific setup steps and Intel OpenMP dependencies. Updated associated build and install scripts to reflect the new toolchain.

Author: allnes

.github/workflows/main.yml

@@ -837,54 +837,51 @@ jobs:
       - uses: actions/checkout@v4
         with:
           submodules: recursive
-      - name: Add msbuild to PATH
-        uses: microsoft/setup-msbuild@v2
+
+      - name: Setup LLVM
+        uses: KyleMayes/install-llvm-action@v1
         with:
-          vs-version: 'latest'
+          version: "17.0"
+
       - name: Setup MPI
         uses: mpi4py/setup-mpi@v1
         with:
           mpi: msmpi
+
       - name: Setup ccache
         uses: Chocobo1/setup-ccache-action@v1
         with:
-          windows_compile_environment: msvc
+          windows_compile_environment: gcc
+
       - name: Setup ninja
         uses: seanmiddleditch/gha-setup-ninja@v6
-      - name: Setup MSVC for Ninja
-        uses: ilammy/msvc-dev-cmd@v1      
-      - name: Install Intel OpenMP via NuGet
-        run: |
-          nuget install intelopenmp.redist.win
-        shell: pwsh
+
       - name: CMake configure
         run: >
           cmake -S . -B build -G Ninja
-          -D CMAKE_C_COMPILER=clang-cl
-          -D CMAKE_CXX_COMPILER=clang-cl
+          -D CMAKE_C_COMPILER=clang
+          -D CMAKE_CXX_COMPILER=clang++
           -D CMAKE_C_COMPILER_LAUNCHER=ccache
           -D CMAKE_CXX_COMPILER_LAUNCHER=ccache
           -D CMAKE_BUILD_TYPE=Release
           -D CMAKE_INSTALL_PREFIX=install
-          -D CMAKE_INCLUDE_PATH="C:/Program Files (x86)/Intel/oneAPI/compiler/latest/windows/include"
-          -D CMAKE_LIBRARY_PATH="C:/Program Files (x86)/Intel/oneAPI/compiler/latest/windows/lib/intel64_win"
-          -D CMAKE_EXE_LINKER_FLAGS="/NODEFAULTLIB:vcomp.lib \"C:/Program Files (x86)/Intel/oneAPI/compiler/latest/windows/lib/intel64_win/libiomp5md.lib\""
-        shell: pwsh
         env:
-          CC: clang-cl
-          CXX: clang-cl
+          CC: clang
+          CXX: clang++
+
       - name: Build project
         run: cmake --build build --config Release --parallel
-        shell: pwsh
         env:
-          CC: clang-cl
-          CXX: clang-cl
+          CC: clang
+          CXX: clang++
+
       - name: Install project
         run: cmake --install build
-        shell: pwsh
+
       - name: Archive installed package
         run: Compress-Archive -Path install -DestinationPath windows-clang-install.zip
         shell: pwsh
+
       - name: Upload installed package
         uses: actions/upload-artifact@v4
         with: