Log Message:
devel/wayland: Patch around -Wundef, __STDC_VERSION, and C++.

Proposed at:

https://mail-index.netbsd.org/tech-pkg/2025/01/15/msg030385.html

Upstream issue:

https://gitlab.freedesktop.org/wayland/wayland/-/issues/522

Upstream commentator suggested taking this branch if __cplusplus
exceeds some threshold too, but I'll leave that to upstream to
decide.