Fix ninja build.
Fix ninja build.

Uses more compatible Windows pathlist separator,
tested with VS2008, VS2012, and Ninja/VS2012

thewtex/python-cmake-buildsystem,msmolens/python-cmake-buildsystem,jcfr/python-cmake-buildsystem,davidsansome/python-cmake-buildsystem,thewtex/python-cmake-buildsystem,adrianbroher/python-cmake-buildsystem,chuckatkins/python-cmake-buildsystem,python-cmake-buildsystem/python-cmake-buildsystem