[Bug c/66658] missing -Wunused-value negating a function result in a comma expression

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66658

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
See also pr64639 (which this bug may be a duplicate of).