The messages you cite are not a problem. That is due to a limitation of wmkdepit doesn't know how to handle #ifdefs (which swak4Foam is heavily contaminated with). To avoid compilation problems on certain platform foam-extend renamed string.H to foamString.H and swak has an #ifdef for that. Which wmkdep doesn't understand and reports but later the real compiler can handle it

So IF there is really a problem you should see it later. Check whether you'd just let yourself be scared by those messages and compilation actually no problem