[Bug middle-end/7651] Define -Wextra strictly in terms of other warning flags

[heiko at hexco dot de via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=7651

--- Comment #40 from Heiko Eißfeldt <heiko at hexco dot de> ---
The example in the previous comment was wrong, sorry!
I don't know how to trigger it.

There seems to be no test case to check for it also.