Support older CMake versions

CMakeLists.txt

@@ -32,7 +32,11 @@ ExternalProject_Add(TUnfold
     URL                 https://www.desy.de/~sschmitt/TUnfold/TUnfold_V17.9.tgz
     URL_HASH            SHA256=d7f66f6a0e007eb946180643b8879bb2b8918441106bc0305b82a97391a391dc
     SOURCE_DIR          "${CMAKE_SOURCE_DIR}/TUnfold"
-    PATCH_COMMAND       "${CMAKE_COMMAND}" -E copy_directory_if_different "${CMAKE_SOURCE_DIR}/cmake/TUnfold" <SOURCE_DIR>
+    PATCH_COMMAND       "${CMAKE_COMMAND}" -E copy_if_different
+                                "${CMAKE_SOURCE_DIR}/cmake/TUnfold/CMakeLists.txt"
+                                "${CMAKE_SOURCE_DIR}/cmake/TUnfold/LinkDef.h.in"
+                                "${CMAKE_SOURCE_DIR}/cmake/TUnfold/TUnfoldConfig.cmake.in"
+                                <SOURCE_DIR>
     CMAKE_ARGS          -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR> -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
     BINARY_DIR          "${CMAKE_SOURCE_DIR}/TUnfold.build"
     INSTALL_DIR         "${CMAKE_INSTALL_PREFIX}"