Fix for CMake MingGW generation.

git-svn-id: http://recastnavigation.googlecode.com/svn/trunk@350 678f7576-1c49-11de-8b5c-13accb87f508
CMake fix - removed hidden variable SDLMAIN_LIBRARY from TARGET_LINK_LIBRARIES, it's not needed.

git-svn-id: http://recastnavigation.googlecode.com/svn/trunk@351 678f7576-1c49-11de-8b5c-13accb87f508