[!547] added missing header to_unique_ptr.hh to CMakeLists.txt
Merge branch 'bugfix/add_to_unique_ptr_to_CmakeLists' into 'master'
Header was missing in CMakeLists.txt and now breaks code due to usage in dune-grid Needs to be backported to 2.6
See merge request core/dune-common!547
(cherry picked from commit 709ea8aa)
53f306b7 added missing header to_unique_ptr.hh to CMakeLists.txt