add test for C++20 compatibility

.github/workflows/check-cpp20.yml

@@ -0,0 +1,92 @@
+# GitHub action to build LAMMPS on Linux with gcc and C++20
+name: "Check for C++20 Compatibility"
+
+on:
+  push:
+    branches:
+      - develop
+  pull_request:
+    branches:
+      - develop
+
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: Build with C++20 support enabled
+    if: ${{ github.repository == 'lammps/lammps' }}
+    runs-on: ubuntu-latest
+    env:
+      CCACHE_DIR: ${{ github.workspace }}/.ccache
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+      with:
+        fetch-depth: 2
+
+    - name: Install extra packages
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y ccache \
+                                libeigen3-dev \
+                                libcurl4-openssl-dev \
+                                mold \
+                                mpi-default-bin \
+                                mpi-default-dev \
+                                ninja-build \
+                                python3-dev
+
+    - name: Create Build Environment
+      run: mkdir build
+
+    - name: Set up ccache
+      uses: actions/cache@v4
+      with:
+        path: ${{ env.CCACHE_DIR }}
+        key: linux-cpp20-ccache-${{ github.sha }}
+        restore-keys: linux-cpp20-ccache-
+
+    - name: Building LAMMPS via CMake
+      shell: bash
+      run: |
+        ccache -z
+        python3 -m venv linuxenv
+        source linuxenv/bin/activate
+        python3 -m pip install numpy
+        python3 -m pip install pyyaml
+        cmake -S cmake -B build \
+              -C cmake/presets/most.cmake \
+              -C cmake/presets/kokkos-openmp.cmake \
+              -D CMAKE_CXX_COMPILER=g++ \
+              -D CMAKE_C_COMPILER=gcc \
+              -D CMAKE_CXX_COMPILER_LAUNCHER=ccache \
+              -D CMAKE_C_COMPILER_LAUNCHER=ccache \
+              -D CMAKE_BUILD_TYPE=Debug \
+              -D CMAKE_CXX_FLAGS_DEBUG="-Og -g" \
+              -D CMAKE_CXX_STANDARD=20 \
+              -D DOWNLOAD_POTENTIALS=off \
+              -D BUILD_MPI=on \
+              -D BUILD_SHARED_LIBS=on \
+              -D BUILD_TOOLS=off \
+              -D ENABLE_TESTING=off \
+              -D MLIAP_ENABLE_ACE=on \
+              -D MLIAP_ENABLE_PYTHON=off \
+              -D PKG_AWPMD=on \
+              -D PKG_GPU=on \
+              -D GPU_API=opencl \
+              -D PKG_KOKKOS=on \
+              -D PKG_LATBOLTZ=on \
+              -D PKG_MDI=on \
+              -D PKG_MANIFOLD=on \
+              -D PKG_ML-PACE=on \
+              -D PKG_ML-RANN=off \
+              -D PKG_MOLFILE=on \
+              -D PKG_RHEO=on \
+              -D PKG_PTM=on \
+              -D PKG_PYTHON=on \
+              -D PKG_QTB=on \
+              -D PKG_SMTBQ=on \
+              -G Ninja
+        cmake --build build
+        ccache -s