Add an interface library for Dune::ISTL

CMakeLists.txt

@@ -25,6 +25,9 @@ include(DuneMacros)
 
 # start a dune project with information from dune.module
 dune_project()
+dune_add_library(duneistl INTERFACE
+  EXPORT_NAME ISTL
+  LINK_LIBRARIES Dune::Common)
 
 add_subdirectory(cmake/modules)
 add_subdirectory(dune)