[Bug c/105499] inconsistency between -Werror=c++-compat and g++ in __extension__ block

[vincent-gcc at vinc17 dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105499

--- Comment #5 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Andrew Pinski from comment #4)
> __extension__ disables all compatibility warnings.
> 
> This is by design really as headers sometimes needs to be written using C
> code and need to turn off these warnings. 

I don't understand why. If the code is designed only for C (i.e. it will not
work with a C++ compiler), then the C++ compatibility option is not needed to
test the code. Otherwise, the code is buggy, so the compatibility warning is
useful.