Compiler path ignored

As per Debian bug https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=834543
How to reproduce: In Tools->Options->Build & Run->Compilers select gcc
and click Clone, then change the compiler path to /bin/cat. Change the
kit's compiler to the newly cloned compiler and compile some .cpp file.
Expected outcome: Qt Creator calls /bin/cat on the .cpp file.
Actual outcome: Qt Creator calls g++ on the .cpp file.

This causes a real problem when you want to compile using clang++-3.8,
because Qt Creator will always use g++ or clang++, ignoring the path set
by the user.