glut: Use a new define GLUT_STATIC to distinguish static builds.

glut: Use a new define GLUT_STATIC to distinguish static builds.

_DLL is defined by MSVC when building against a DLL version of the CRT
library. It bears no relation to whether we are building a DLL or not. That
is, we can build a DLL against a static CRT, or a static lib against a
dynamicaly linked CRT. See more detail at
http://msdn.microsoft.com/en-us/library/2kzt1wy3.aspx

This gets DLL version of glut linking correctly both with MinGW and MSVC.

PS: GL/gl.h (and others) must be fixed too.