I thought there was a request function for this. I just checked the manual and see that there is a function for the GDL compiler version and another for the name of the program (i.e. "ArchiCAD"), but none for the ArchiCAD version number.
It appears that this is not possible unless there is an undocumented function for it.
This may be due to the incompatibility of GDL from one version of ArchiCAD to the next (ArchiCAD 6.5 to 7.0 was the sole exception in my experience). The GDL version is automatically checked by the program so it's not clear what purpose it would serve in writing library parts. It certainly matters for the API, but I assume there is a function for this there.
