lrwxrwxrwx 1 root root 3 Oct 30 12:52 /usr/lib64 -> lib/
lrwxrwxrwx 1 root root 7 Oct 30 12:52 /lib -> usr/lib/
So anything going to /usr/lib64 end up in /usr/lib, unless you have removed the links intentionally. Otherwise there is no difference from arch. Alternatively you can use the .configure on the pkg to direct the libraries to /usr/lib
But I see the comment section is full of your debate with the Klingons that run arch public relations. They feed off heretics not doing things their way or using pkgs outside their control. From one side they consider AUR as not part of arch, but on the other hand they CONTROL AUR as being solely for the use of Arch. Meanwhile they have 3-4-5 year old unmaintained versions of runit and openrc on AUR, but anyone trying to use anything but systemd is NOT arch.
So why bother even talking to those bozos?
I use yaourt, and in all the years I use to makepkg PKGBUILDs and then pacman -U ***.xz has never had a different outcome of yaourt. ARCHers hate yaourt. They now hate trizzen too, but that huge blob of crap they call yay is now a good thing. Still it is not arch officially.
The PKGBUILD is messed up, nothing wrong with trizzen or your obarun.