cmake: use keyword signature of `target_link_libraries`

dune-common switched to using the keyword signature and mixing keyword and plain signatures causes a CMake error:

CMake Error at [...].cmake:[...] (target_link_libraries):
  The keyword signature for target_link_libraries has already been used with
  the target "[...]".  All uses of target_link_libraries with a target
  must be either all-keyword or all-plain.