[Bug target/94770] class with empty base passed incorrectly with -std=c++17 on mingw

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94770

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
At least, when using:
gcc version 9.2.1 20190827 (Fedora MinGW 9.2.1-1.fc31) (GCC) 
and executing with Wine.