Alex Turbov authored Jun 03, 2020 and Brad King committed Jun 15, 2020

CPack learned the `CPACK_PRE_BUILD_SCRIPTS`, `CPACK_POST_BUILD_SCRIPTS`,
and `CPACK_PACKAGE_FILES` variables.

The first two are lists of scripts to perform
- after pre-install files into a staging directory and before
  producing the resulting packages
- after produsing the packages

The post-build script(s) also get the list of actually produced
packages in the `CPACK_PACKAGE_FILES`.

Issue: #19077