Works for me. What are your /tmp permissions after installing the filesystem package? That's where the <<< used in lines 268 and 272 will be creating a temporary file with random name. It's odd that it would be returning an errno=0 instead of EPERM, though.
Hi Linas, First of all, sorry for the (very) late reply and thanks for your interest, there were some not so good changes in my life lately and I couldn't answer early :) Following your suggestion I did some research on this issue and this is what I found: /tmp folder permissions are the same after installing the new package, however (and this is the real thing) I found every normal user in the system are given root privileges, that's why makepkg fails, because it tries to compile the package as root; if I launch makepkg with --asroot argument it while run ok. I found too that adding a new user after upgrading core/filesystem it's created as expected without any issues. Anyways, if no problem arise I think I will wait until next package update and try to upgrade it but in the event it's totally necessary to upgrade this package seems I will need to do that 'trick' of creating a new user after upgrading and migrating my actual user to the new one. Thank you very much again! Last, wish you all people the best for the upcoming year: Happy New Year! =D