Do not activate aöö packages by default in the Eigen backend

CMakeLists.txt

@@ -23,7 +23,6 @@ add_subdirectory("libs")
 dune_add_library(amdis
   LINK_LIBRARIES ${DUNE_LIBS} fmt::fmt
   EXPORT_NAME AMDiS NAMESPACE AMDiS::)
-add_dune_all_flags(amdis)
 
 add_subdirectory("amdis")
 add_subdirectory("bin")
@@ -48,6 +47,11 @@ if (PETSc_FOUND)
   target_link_libraries(amdis PUBLIC PETSc::PETSc)
 endif (PETSc_FOUND)
 
+if (NOT EIGEN3_FOUND)
+  # do not activate all packages by default in the Eigen backend
+  add_dune_all_flags(amdis)
+endif()
+
 
 if (ENABLE_ALL_WARNINGS)
   target_compile_options(amdis PUBLIC "-Wall" "-Wpedantic"