cmake-lib.bbclass: rework
cmake-lib.bbclass: rework

* break linḱs to image directory for cmake files to fix race with
  do_package and double replacements when restoring from sstate
* avoid double replacements so that they work for sysroot paths imported
  from other packages
* documentation

Signed-off-by: Andreas Müller <d72a15aaaca3a7afa855175c72dc8d2e05931e32@googlemail.com>

schnitzeltony/meta-qt5-extra,schnitzeltony/meta-qt5-extra,schnitzeltony/meta-qt5-extra