Usually you use a turntable (not the DJ ones, rather a moving plate) on which you place a chair to sit on. Then you record IRs at each position (turning the table, leaving the loudspeaker where it is). Be careful not to move too much. Moving the loudspeaker up and down lets you record different heights. And yes, the room is part of the impulse response, so for a true HRTF you're going to record it in a "dead room". sweeps are common practice as far as I know.. Lots of work :)