I'll note it never worked for me. I could build Qt5. Takes a lot of memory, VIRTUALADDRESSLIMIT=3072 and with 3.2 GB's of visible memory here, there was swapping, so make sure you have a swapfile, weird popups about no memory and the need to reboot the odd time to recapture memory, fragmentation I assumed. Took almost a day here as well, being careful not to run things like browsers.