Apply -Wno-inconsistent-missing-override for all compilers
Summary:
Default CXX flags are out of our control. Whether they're set by the
compiler or the user or ECM.
We currently disable for clang. This patch also disables this warning
for other compilers.
This might not be anyone's first preference, but we're at an impasse
there.
Test Plan: Compiled
Reviewers: KWin, graesslin
Reviewed By: KWin, graesslin
Subscribers: zzag, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D18488