If an undefined function is called and we create a temporary variable,
the type of this variable was "void".
It needs to be "int" because this is the default return type for
undefined functions.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14383 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c