osdemos: use gl_wrap.h instead of glut_wrap.h
If we attempt to build these without having found GLUT, we end up failing due to missing the GLUT headers. But these demos doesn't actually use GLUT, so let's just switch to another wrapper here.
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If we attempt to build these without having found GLUT, we end up failing due to missing the GLUT headers. But these demos doesn't actually use GLUT, so let's just switch to another wrapper here.