The gcc release tarball is only 60M in size, while makepkg is now forced to clone the entire gcc git repository, at over 2G in size, to build the package. Because most people do not have gigabit connections, this considerably slows down the build process. For me, the git clone alone takes over 20 minutes (!) to download everything and index it. Please try to reduce this by either using gcc's official releases or at the very least by doing a shallow clone.