Squashed 'CMakeModules/' changes from e83ac80..ebfa49d

ebfa49d Merge pull request #1 from arpg/private_linkage
40245bc Makes def_library link privately.
2979d55 Fix install when version string is empty.

git-subtree-dir: CMakeModules
git-subtree-split: ebfa49d8c26ef31a783425596febca3f457820ec
Merge commit 'b6ea72d690ca73fc21addcb57d458e10b3e5005d'
Merge pull request #9 from arpg/private_linkage

Updates def_library.