[!815] assign a true value to `ENABLE_UMFPACK`

Merge branch 'assign-true-value-to-ENABLE_UMFPACK-macro' into 'master'

See merge request [!815]

  [!815]: Nonecore/dune-common/merge_requests/815

cmake/modules/AddUMFPackFlags.cmake

@@ -18,7 +18,7 @@ function(add_dune_umfpack_flags _targets)
       get_target_property(_props ${_target} COMPILE_FLAGS)
       string(REPLACE "_props-NOTFOUND" "" _props "${_props}")
       set_target_properties(${_target} PROPERTIES COMPILE_FLAGS
-        "${_props} ${UMFPACK_DUNE_COMPILE_FLAGS} -DENABLE_UMFPACK")
+        "${_props} ${UMFPACK_DUNE_COMPILE_FLAGS} -DENABLE_UMFPACK=1")
     endforeach(_target ${_targets})
   endif(UMFPACK_FOUND)
 endfunction(add_dune_umfpack_flags)