Automatically set the with_mpi option from CMake using command line arguments

cmake/modules/DuneCodegenMacros.cmake

@@ -116,6 +116,11 @@ function(dune_add_generated_executable)
     message(FATAL_ERROR "Unrecognized arguments in dune_add_generated_executable. This usually indicates a typo.")
   endif()
 
+  set(MPI_OPTION "0")
+  if(MPI_FOUND)
+    set(MPI_OPTION "1")
+  endif()
+
   # Apply defaults and enforce requirements
   if(NOT GEN_TARGET)
     message(FATAL_ERROR "Need to specify the TARGET parameter for dune_add_generated_executable")
@@ -139,6 +144,7 @@ function(dune_add_generated_executable)
                                --target-name ${GEN_TARGET}
                                --driver-file ${GEN_SOURCE}
                                --project-basedir ${CMAKE_BINARY_DIR}
+                               --with-mpi ${MPI_OPTION}
                                ${GEN_FORM_COMPILER_ARGS}
                        DEPENDS ${GEN_UFLFILE} ${UFL2PDELAB_SOURCES} ${GEN_DEPENDS} ${DUNE_CODEGEN_ADDITIONAL_PYTHON_SOURCES}
                        COMMENT "Generating driver for the target ${GEN_TARGET}"
@@ -199,6 +205,7 @@ function(dune_add_generated_executable)
                                --ini-file ${GEN_INIFILE}
                                --target-name ${GEN_TARGET}
                                --operator-to-build ${op}
+                               --with-mpi ${MPI_OPTION}
                                ${ANALYZE_GRID_OPTION}
                        DEPENDS ${GEN_UFLFILE} ${UFL2PDELAB_SOURCES} ${GEN_DEPENDS} ${DUNE_CODEGEN_ADDITIONAL_PYTHON_SOURCES} ${ANALYZE_GRID_FILE}
                        COMMENT "Generating operator file ${depdata___${op}} for the target ${GEN_TARGET}"