title: Multiple debian packages without dependencies pollution
body: <p>I am trying to create multiple debian packages using CPack. I have been following the documentation from:</p>
  <ul>
  <li><a href="https://gitlab.kitware.com/cmake/community/-/wikis/doc/cpack/Component-Install-With-CPack" rel="nofollow noreferrer">https://gitlab.kitware.com/cmake/community/-/wikis/doc/cpack/Component-Install-With-CPack</a></li>
  </ul>
  <p>and</p>
  <ul>
  <li><a href="https://cmake.org/cmake/help/latest/module/CPackComponent.html" rel="nofollow noreferrer">https://cmake.org/cmake/help/latest/module/CPackComponent.html</a></li>
  </ul>
  <p>However it seems that any <code>install(COMPONENT)</code> is being considered for the final packages, including those defined under a <code>add_subdirectory(EXCLUDE_FROM_ALL)</code>.</p>
  <p>Consider the following simple cmake structure:</p>
  <pre><code>% cat CMakeLists.txt
  cmake_minimum_required(VERSION 3.18)
  project(p)
  add_subdirectory(dep EXCLUDE_FROM_ALL)
  
  # define our install + component
  install(FILES main.py
    DESTINATION main
    COMPONENT main-comp
    )
  
  # multiple deb package is desired:
  set(CPACK_DEB_COMPONENT_INSTALL ON)
  
  # disable not needed:
  set(CPACK_BINARY_STGZ OFF)
  set(CPACK_BINARY_TZ OFF)
  set(CPACK_SOURCE_TGZ OFF)
  #
  set(CPACK_BINARY_DEB ON)
  set(CPACK_PACKAGE_CONTACT foo@bar.com)
  include(CPack)
  </code></pre>
  <p>and</p>
  <pre><code>% cat dep/CMakeLists.txt
  install(FILES dep.txt
    DESTINATION dep
    COMPONENT remove-me
    )
  </code></pre>
  <p>With:</p>
  <pre><code>% touch main.py dep/dep.txt
  </code></pre>
  <p>On my debian machine (buster) here is what I see:</p>
  <pre><code>% make package
  [...]
  CPack: - package: /tmp/p/bin/p-0.1.1-Linux-main-comp.deb generated.
  CPack: - package: /tmp/p/bin/p-0.1.1-Linux-remove-me.deb generated.
  </code></pre>
  <p>I have no interest in the package related to COMPONENT <code>remove-me</code>, is there a way to discard it completely for the list of debian packages to be generated.</p>
  <p>For reference:</p>
  <pre><code>% cmake --version
  cmake version 3.18.4
  </code></pre>
  <hr />
  <p>Use case is where <code>dep</code> is actually a <code>git remote</code> repository which I am not able to modify (consider it read-only).</p>