I'm trying to compile r179 and I'm getting lots of errors. Because of the errors, the compile is going slowly, so I just cancelled it so I don't know what happens further one. However, all the errors so far mention this:
It's not in the GZdoom directory. However, on checking Zdoom, there is a file in there of the same name. I don't know if the file is meant to be identical in the two projects but, whether it is or not, it seems that it is missing from GZdoom.