build: repair the build on 14.04

CMake 3.4.3 does not support the <files>... <directory> pattern for
copy_if_different.  Adjust for that.

Author: compnerd

CMakeLists.txt

@@ -414,7 +414,7 @@ if(ENABLE_TESTING)
                      BYPRODUCTS
                        ${CMAKE_CURRENT_BINARY_DIR}/TestFoundation/xdgTestHelper${CMAKE_EXECUTABLE_SUFFIX}
                      COMMAND
-                       ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_BINARY_DIR}/xdgTestHelper${CMAKE_EXECUTABLE_SUFFIX} ${CMAKE_CURRENT_BINARY_DIR}/TestFoundation
+                       ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_BINARY_DIR}/xdgTestHelper${CMAKE_EXECUTABLE_SUFFIX} ${CMAKE_CURRENT_BINARY_DIR}/TestFoundation/xdgTestHelper${CMAKE_EXECUTABLE_SUFFIX}
                      DEPENDS
                        TestFoundation
                        xdgTestHelper)