cmake_minimum_required(VERSION 3.12)

file(WRITE foo/CMakeLists.txt [[
    install(FILES CMakeLists.txt DESTINATION foo)
    install(CODE "message(foo!!!)")
]])

file(WRITE bar/CMakeLists.txt [[
    install(FILES CMakeLists.txt DESTINATION bar)
    install(CODE "message(bar!!!)")
]])

add_subdirectory(foo)

add_subdirectory(bar)

install(CODE "message(baz!!!)")

######################################

cmake -DCMAKE_INSTALL_PREFIX=/home/ngladitz/src/test/ins/build/inst -P cmake_install.cmake
-- Install configuration: ""
baz!!!
-- Up-to-date: /home/ngladitz/src/test/ins/build/inst/foo/CMakeLists.txt
foo!!!
-- Up-to-date: /home/ngladitz/src/test/ins/build/inst/bar/CMakeLists.txt
bar!!!