Correct cmake setup to include headers - cmake

Question

I have a project structured like this:
─root
├──src
│ ├──main.cpp
│ └──CMakeLists.txt[2]
├──build
├──out
├──inc
├──dep
│ ├──log
│ │ ├──include
│ │ │ └──log.h
│ │ ├──src
│ │ │ └──log.cpp
│ │ └──CMakeLists.txt[4]
│ └──CMakeLists.txt[3]
└──CMakeLists.txt[1]
Under dep I have a logging library, which is an external git repository with his own CMakeLists.txt file.
The main CMakeLists.txt (marked as [1]) is:
cmake_minimum_required(VERSION 2.6)
set(APP_ROOT ${PROJECT_SOURCE_DIR})
add_subdirectory(dep)
add_subdirectory(src)
The CMakeLists.txt (marked as [2]) for the current project code is:
add_executable(app main.cpp)
target_link_libraries(app log)
include_directories("${APP_ROOT}/inc")
The CMakeLists.txt (marked as [3]) for the dependencies is:
add_subdirectory(log)
What I'm trying to do is to have the contents of the dep/log/include folder copied inside a new folder called inc/log, so that in main.cpp I can write something like #include <log/log.h>, but I don't understand how. I would like to avoid editing the CMakeLists.txt of the logger project.

Answer 1

My solution: in /dep/CMakeLists.txt I added
file(MAKE_DIRECTORY "${APP_ROOT}/inc/log")
file(COPY "log/include/" DESTINATION "${APP_ROOT}/inc/log")