On 64bit Linux systems, you will have to install 32bit compatibility libraries to run QCAD. Most 64bit Linux distributions have one single package you need to install to provide 32bit compatibility, usually called "ia32-libs". Archlinux seems to offer a similar way which is described in detail on the Archlinux web site at:https://wiki.archlinux.org/index.php/Us ... _on_Arch64
You will most likely only need these two pieces of information:
Programs using QT should run at once after installing lib32-qt.
Library paths without having them in /etc/ld.so.conf