MINOR: debug: make BUG_ON() catch build errors even without DEBUG_STRICT

MINOR: debug: make BUG_ON() catch build errors even without DEBUG_STRICT

As seen in previous commit 59acb27001 ("BUILD: quic: Variable name typo
inside a BUG_ON()."), it can sometimes happen that with DEBUG forced
without DEBUG_STRICT, BUG_ON() statements are ignored. Sadly, it means
that typos there are not even build-tested.

This patch makes these statements reference sizeof(cond) to make sure
the condition is parsed. This doesn't result in any code being emitted,
but makes sure the expression is correct so that an issue such as the one
above will fail to build (which was verified).

This may be backported as it can help spot failed backports as well.