Implement separate Fortran and C++ Drivers.

Provide Fortran driver with OpenACC to test portability close to the ICON use-case.

CMakeLists.txt

 cmake_minimum_required(VERSION 3.20)
-project(demo LANGUAGES CXX VERSION 0.0.1)
+project(demo LANGUAGES CXX Fortran VERSION 0.0.1)
 
 
 include(FetchContent)
@@ -36,9 +36,28 @@ endif()
 
 FetchContent_MakeAvailable(kokkos)
 
-add_executable(demo main.cpp)
+add_executable(demo cdriver.cpp main.cpp)
 target_link_libraries(demo PUBLIC Kokkos::kokkos)
 
+set_source_files_properties(
+  fdriver.f90
+  PROPERTIES Fortran_PREPROCESS ON
+)
+
+if (Kokkos_ENABLE_CUDA OR Kokkos_ENABLE_HIP)
+  set(WITH_OPENACC_FORTRAN 1)
+else()
+  set(WITH_OPENACC_FORTRAN 0)
+endif()
+
+add_executable(fdemo fdriver.f90 main.cpp)
+target_link_libraries(fdemo PUBLIC Kokkos::kokkos)
+if (WITH_OPENACC_FORTRAN)
+  find_package(OpenACC REQUIRED OpenACC_Fortran)
+  target_link_libraries(fdemo PUBLIC OpenACC::OpenACC_Fortran )
+endif()
+set_property(TARGET fdemo PROPERTY LINKER_LANGUAGE Fortran)
+
 if ("${MU_ARCH}" STREQUAL "a100")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -acc -Minfo=accel -gpu=cc80")
     add_compile_definitions(DEMO_DEVICE)