Link handling gcc works somewhat different from other debian packages, and has own reasons for it.
In other packages there are the alternatives system that can be configured to point to correct executables. gcc is seen as a system program that shouldn't be changed. See http://bugs.debian.org/107587
In sort, you shouldn't do it. If you still think you want to have gcc overridden, you can do it; you have been warned.
dpkg-divert --rename --divert /usr/bin/gcc.dpkg /usr/bin/gcc
Now the gcc file is left alone by the packaging system (original gcc is now known with the name gcc.dpkg).