[Bug c++/85091] Compiler generates different code depending on whether -Wnonnull -Woverloaded-virtual given or not

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85091

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I can't reproduce this with:
gcc version 7.2.0 20170814 (Fedora MinGW 7.2.0-1.fc26) (GCC) 

I get one warning:

$ i686-w64-mingw32-g++ -c -std=c++17 -Wnonnull -Woverloaded-virtual -O2
16795.cpp
16795.cpp: In function 'unsigned int _get_output_format()':
16795.cpp:316:25: warning: 'unsigned int _get_output_format()' redeclared
without dllimport attribute: previous dllimport ignored [-Wattributes]
 extern "C" unsigned int _get_output_format(void) {return 1;}
                         ^~~~~~~~~~~~~~~~~~

But no different code depending on the warning options used.