Still build even if CPACK_GENERATOR is undefined
Still build even if CPACK_GENERATOR is undefined

Without the quotes around `${CPACK_GENERATOR}`, Windows CMake, generating
for VS2013, would exit with an error because the `STREQUAL` only had one arg.

scrawl/osg,openscenegraph/osg,openscenegraph/osg,openscenegraph/osg,scrawl/osg,scrawl/osg,openscenegraph/osg,scrawl/osg