Add -Werror=switch and -Wcovered-switch-default
Summary:
The former ensures that switch statements are adapted when an
enumeration is changed. The latter encourages to remove the default
label in fully covered switch statements, making the former more
effective. (It is silenced by default labels.)
Reviewers: KDevelop, mwolff
Reviewed By: KDevelop, mwolff
Subscribers: mwolff, apol, kdevelop-devel
Differential Revision: https://phabricator.kde.org/D9042