Back in 1.2.6 and earlier, I was able to build a cross compile of LCL with this command run in source root for each OS/CPU/widgetset I chose:
lazbuild --ws=GUI_TYPE --os=OS_TYPE --cpu=CPU_TYPE lcl/lclbase.lpk
lazbuild --ws=GUI_TYPE --os=OS_TYPE --cpu=CPU_TYPE lcl/interfaces/lcl.lpk
However, this seems to have changed in 1.4.0. Lazbuild complains that these .lpk files do not exist.
primary config path: /home/admin/.lazarus
Error: invalid Lazarus directory "": directory lcl not found
Failed building lcl/lclbase.lpk
EDIT: solved, please remove