Fixed CMake UNIX config when building only "freeglut_static" or only the shared library

 - was setting a property on "freeglut" while "FREEGLUT_BUILD_SHARED_LIBS" was "OFF"

git-svn-id: https://svn.code.sf.net/p/freeglut/code/trunk@1638 7f0cb862-5218-0410-a997-914c9d46530a
Merge branch 'svn/trunk'