osd: Add OSD_API and OSD_TEMPLATE define for exporting symbols on Windows

Clients of the OSD library will need to define OSD_DLL if they want to
dynamically link against the OSD library.
cmake: Add OSD_DLL defines to examples and regressions
osd: Export some classes and methods for Windows DLL
TEMP: favor dynamic GLEW

TODO: Need a way to decide which one to use.