Sources/CMakeLists.txt: Added missing find_packge(SDL REQUIRED) to link in the SDL1.2 libraries via ${SDL_LIBRARY} generate variable
and added to the target_link_libraries for SeriousSam and SeriousSamDedicated. I don't know not linking the SDL library was
the intended outcome but SeriousSam* was failing to link to libSeriousEngine.a.
Sources/CMakeLists.txt: Added missing find_packge(SDL REQUIRED) to link in the SDL1.2 libraries via ${SDL_LIBRARY} generate variable