Add Function Definition leaves out "struct" for C files

Right now Qt Creator can be used to edit pure C projects, but that's only possible if the user shoehorns support for C++ to adapt to C's needs. However, that hack only goes so far as some features break in some form or another.

For example, Qt Creator enables adding function definitions to C source files, but if the function is declared to accept structs as inputs the auto-generated function definition will leave out the "struct". That strategy might be valid with C++ but by omitting the "struct" the function definition ceases to be valid C.