Log Message:
boost: Add target for CMake files

pkgsrc changes:
---------------
  * The FindBoost module of CMake is removed since version 3.30
    (https://cmake.org/cmake/help/v3.30/policy/CMP0167.html). Upstream
    Boost provides CMake files as replacement since version 1.70. Add a
    target to install these files in ${DESTDIR}.
  * This target uses an extra file cmake-dirs.mk to list the subdirectories
    in lib/cmake/. But a more automatic method should be considered...