[Bug c++/69723] pre-post-increment/decrement and reading the same variable that is assigned should not be considered uses for Wunused-but-set-variable

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69723

--- Comment #8 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #7)
> As for the missed -Wuninitialized at -O0, wonder if we couldn't do something
> about it for GCC 7.

Sounds good to me, but perhaps it is better to open a new PR. This one is a bit
messy (and closed as a duplicate).