Revert "setup.py: skip adding gcc warnings flags with msvc. Fixes #275"
Revert "setup.py: skip adding gcc warnings flags with msvc. Fixes #275"

This reverts commit f7503c4cd1c03fde215024e61db9e1a439f39997.

GNOME/pygobject,GNOME/pygobject,GNOME/pygobject