[arch-general] makepkg default flags

A few months back there was a proposal to edit the default makepkg build flags for improved security: https://lists.archlinux.org/pipermail/arch-dev-public/2020-July/030031.html As far as I can tell, this was never committed. The show-stopper at the time was Clang 11 not being released yet. Now that it's been in the repos for a while, could we revisit this improvement and possibly get a mass rebuild with it applied?