Prepare for x86_64-v3 repos

[wszqkzqk]

Arch Linux developers discussed to start x86_64-v3 port, openSUSE has launched this and Fedora also has planed to add x86-64 v2/v3/v4 feature levels. Is it necessary for MSYS2 to add x86_64-v3 feature level for performance?

[MehdiChinoune]

I proposed that before, they had a discussion about it in a previous meeting.
Most of maintainers have no interest on the idea.

see: https://pads.c3w.at/code/#/2/code/edit/oXdtR5THJy75DZIllZBAnEHw/ -> 2021-11-07

MinGW-x86_64-v3?
- minimum CPU level in our mingw repos should cover what supported Windows version covers; once we drop support of some Windows version, we can bump CPU level accordingly
- doesn't seem like worth the effort to maintain separate package repo
- we can recommend the user to maintain an unofficial repo with just the packages that are really faster with v3 and we can link to it on msys2.org for speed enthusiasts :)

They maintain two separate repos for expired/outdated/non-used 32bit arch, but couldn't maintain a repo for ~70% (at least) of users!