QtCreator should cleanup/prevent core dumps from clang backend

Our source code configuration happens to have some source code which doesn't play well with Creator's clang source code model which sometimes leads to crashes of the clang-background process. It would be barely noticeable but on our development PCs "ulimit -c unlimited" is called and therefore, when working on a problematic source file, the hard disk can get filled up on core dumps pretty quickly.
Therfore I propose either add "ulimit -c 0"  in bin/qtcreator.sh or call the apropriate functions before exec the backend process.