Yes, because it is defined by glgsg.h, which defines all of the relevant macros (including CLP), and then includes glGraphicsStateGuardian_src.h. This is the same way that the linmath directory works, which works fine with interrogate, so I see no reason why it shouldn’t also work with interrogate here.
The point is that you can’t interrogate glGraphicsStateGuradian_src.h, or anything in glstuff, directly; those files aren’t meant to be read in isolation. You can only interrogate glgsg.h and the other files in the glgsg directory.
David