r300 likely broken absent -Dlegacy-x11=dri2

Description:

The mesa package isn't compiled w/ -Dlegacy-x11=dri2 but some hardware resp. their mesa drivers are incapable of DRI3

Additional info:

• package version(s): 24.3 and up
• link to upstream bug report, if any: https://gitlab.freedesktop.org/mesa/mesa/-/issues/12024#r300-driver
• BBS thread of affected user: https://bbs.archlinux.org/viewtopic.php?id=306221

Steps to reproduce:

1. Have a r300 chip
2. update to any recent mesa >= 24.3
3. run glxinfo
4. notice that you're on software emulation