Don't add 'override' specifier for non-modern project settings
Summary:
Override code completion will only add the override specifier if the parser
settings don't have either -std=c++03 or 98.
Supersedes: D4039
BUG: 372280
Test Plan: Run test_codecompletion testOverrideExecute
Reviewers: kfunk
Reviewed By: kfunk
Subscribers: kfunk, kdevelop-devel
Tags: KDevelop
Differential Revision: https://phabricator.kde.org/D16773
(cherry picked from commit 0636cfdd8a93617cbcf2efe2c9d74eab21a0b97b)