Add -Woverloaded-virtual to -Wall

[Michel Zou via Gcc-patches]

Hi,

Here is a patch to add -Woverloaded-virtual to -Wall:
https://gcc.gnu.org/bugzilla/attachment.cgi?id=49021

It should address this:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87729

Regards,