[CMake] install DuneSymlinkOrCopy.cmake

This macro was split off from DuneMacros.cmake in commit
e63ea0cf, but the new macro file was
not included in the list of installed macros.

cmake/modules/CMakeLists.txt

@@ -15,6 +15,7 @@ set(modules
   DuneMPI.cmake
   DunePkgConfig.cmake
   DuneStreams.cmake
+  DuneSymlinkOrCopy.cmake
   DuneTestMacros.cmake
   DuneTests.cmake
   FindBoostFusion.cmake