Squashed 'CMakeModules/' changes from 2979d55..ebfa49d

ebfa49d Merge pull request #1 from arpg/private_linkage
40245bc Makes def_library link privately.

git-subtree-dir: CMakeModules
git-subtree-split: ebfa49d8c26ef31a783425596febca3f457820ec
Merge commit '9616d58fb6e74e9305ce2f07605049a27d9b015f' into HEAD
Merge pull request #1 from arpg/private_linkage

Updates def_library.