macOS: fix build with Xcode 9.3 (clang 9.1.0)
macOS: fix build with Xcode 9.3 (clang 9.1.0)

mcallegari/qlcplus,plugz/qlcplus,mcallegari/qlcplus,sbenejam/qlcplus,sbenejam/qlcplus,sbenejam/qlcplus,sbenejam/qlcplus,plugz/qlcplus,kripton/qlcplus,plugz/qlcplus,kripton/qlcplus,kripton/qlcplus,sbenejam/qlcplus,mcallegari/qlcplus,mcallegari/qlcplus,mcallegari/qlcplus,plugz/qlcplus,plugz/qlcplus,plugz/qlcplus,kripton/qlcplus,sbenejam/qlcplus,kripton/qlcplus,mcallegari/qlcplus,mcallegari/qlcplus,plugz/qlcplus,kripton/qlcplus,sbenejam/qlcplus,kripton/qlcplus