Are you compiling with the current table builds i.e 1.6.2/300/302 or 1.6.4/300/302?
Did you compile it with another projects or the vclua project itself? Perhaps it could be down to some projects settings in vclua which is a dll/so.
I did a full IDE build. Afaik that builds the entire package.
Build with tagged versions 3.0.2, and 1.6.4 (Actually, build with the official 1.6.4 win 64 bit release binaries / the fpc included is build from svn, not taken from the fpc release bin, but that is the case for all past lazarus releases.)
I just compiled a new empty project, to which I added the unit. no problems (on 64 bit). And the unit definitely got compiled, if I put an error in there, then it fails, if I remove it again, then it compiles.
I only tested windows. and intel. Not sure about other targets.
It looks as if for some reason your fpc does not think of LongInt as 32 bit signed integer.
Or some setting affects, the sizeof(set)