Fix EcmGenerateExportHeader tests on Windows
Summary: -weXXXX errors on warning XXXX. C4996 warns on deprecated declarations.
Test Plan: Tests pass.
Reviewers: kossebau, Windows, Frameworks
Reviewed By: kossebau
Subscribers: kde-frameworks-devel, kde-buildsystem
Tags: Frameworks, Build System
Differential Revision: https://phabricator.kde.org/D25626