makepkg.conf: Increase _FORTIFY_SOURCE level to 3

kpcyrd requested to merge kpcyrd/devtools:rfc-0017-increase-fortify-level into master

This is the relevant change for RFC 0017-increase-fortification-level that was merged 4 months ago.

Fedora and OpenSUSE also switched to level 3 in 2023.

Relevant TODO list: https://archlinux.org/todo/prepare-packages-for-d_fortify_source3/

Edited by kpcyrd

Merge request reports