Tracking issue: x86_64 backend miscompiles river

[ifreund]

As of commit cf059ee, the native x86_64 backend miscompiles river. The most obvious symptoms are keyboard input not reaching wayland clients and keyboard bindings in the compositor not working.

This used to work in Zig 0.13.0, so this seems to be a regression.

This issue is open to remind us to test the backend on river again before enabling it by default.