Merge branch 'cherry-pick-cb78595c' into 'releases/3.6'

Merge branch 'feature/set-multithreading-backend-cmake-opts' into 'master'

See merge request !3325

cmake.opts

@@ -45,6 +45,11 @@ DUMUX_ENABLE_HEADERCHECK=OFF
 DUMUX_ENABLE_PYTHON_BINDINGS=""
 #DUMUX_ENABLE_PYTHON_BINDINGS="-DDUNE_ENABLE_PYTHONBINDINGS=1 -DBUILD_SHARED_LIBS=1"
 
+# set multithreading backend, e.g. OpenMP,TBB,Cpp,Kokkos,Serial
+# if left empty, it is automatically set by cmake
+DUMUX_MULTITHREADING_BACKEND=""
+#DUMUX_MULTITHREADING_BACKEND="-DDUMUX_MULTITHREADING_BACKEND=OpenMP"
+
 # for debug opts you can set DCMAKE_BUILD_TYPE to "Debug" or "RelWithDebInfo"
 # you can also do this in any of the CMakeLists.txt in Dumux
 # just rerun cmake again afterwards (run cmake <path-to-build-dir>)
@@ -56,5 +61,6 @@ CMAKE_FLAGS="$SPECIFIC_COMPILER $SPECIFIC_GENERATOR $OPM_FLAGS
 -DCMAKE_BUILD_TYPE=Release
 -DENABLE_HEADERCHECK=$DUMUX_ENABLE_HEADERCHECK
 $DUMUX_ENABLE_PYTHON_BINDINGS
+$DUMUX_MULTITHREADING_BACKEND
 $DUMUX_CMAKE_FLAGS
 "