Fixed build issues for Clang 6.0 on OS X

Hello Daniel!

This changeset fixes build issues which I faced on OS X 10.9 with Clang 6.0, trying to build cppcheck-gui.
Build checked also on Linux(gcc 4.8). Unfortunately, I can not check build on Windows at the moment.

If something's wrong with my changest -- please, let me know and I'll fix it.

With best regards,
Andrew Shelestov