Support external consumption of ROOT_LINKER_LIBRARY
Support external consumption of ROOT_LINKER_LIBRARY

If one calls the ROOT_LINKER_LIBRARY macro from an external project
after a cmake include(${ROOT_USE_FILE}), the build fails, because of the
missing move_headers target, which is defined in a ROOT project specific
CMakeLists.txt file. This commit will add the dependency to the
move_headers target only, if the macro is called from withing the ROOT
project.

olifre/root,root-mirror/root,olifre/root,olifre/root,zzxuanyuan/root,zzxuanyuan/root,olifre/root,karies/root,karies/root,olifre/root,olifre/root,root-mirror/root,zzxuanyuan/root,zzxuanyuan/root,olifre/root,karies/root,zzxuanyuan/root,olifre/root,karies/root,karies/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,zzxuanyuan/root,karies/root,karies/root,root-mirror/root,zzxuanyuan/root,root-mirror/root,root-mirror/root,zzxuanyuan/root,zzxuanyuan/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,root-mirror/root,karies/root,olifre/root,zzxuanyuan/root,root-mirror/root,zzxuanyuan/root,zzxuanyuan/root,karies/root