How I can install some gcc compilers in arch linux?

I need to install earlier gcc than now. I already have gcc-10. I must install gcc-8 or gcc-6 in my computer then to build old project. I download the gcc-6 from github and tried install it as shown in this guide https://gist.github.com/slizzered/a9dc4e13cb1c7fffec53 . I got the error: target not found: libart-lgpl . Google was show me than it's error occurs due to than this package is't contents from main repository. Stop! Ones again. If I want to build gcc-6 then I need to download and install yaourt then next install libart-lgpl which is not in the official repository? Pleas help my download & install some gcc compilers from my computer.