cmake_minimum_required(VERSION 3.4)

project(Foo)

file(WRITE sub/CMakeLists.txt [[
    add_library(mylib INTERFACE IMPORTED GLOBAL)

    set_property(TARGET mylib PROPERTY
        INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_BINARY_DIR}
    )
]])

add_subdirectory(sub)

file(WRITE myexe.cpp "int main() {}")
add_executable(myexe myexe.cpp)
target_link_libraries(myexe PRIVATE mylib)