Fix bugfix for #178:
When looking at function types, we need to get the canonical type
to resolve typedefs, but we may not resolve the parameter types,
because otherwise elaborated types in the parameters get resolved
to struct types, and this produces illegal C code.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14031 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c