for a nested function 'fd' return the type of the closure of an outer function or aggregate. If the function is a member function the 'this' type is expected to be stored in 'sthis.Sthis'. It is always returned if it is not a void pointer. buildClosure() must have been called on the outer function before.
.backend .type .TYPE* getParentClosureType (
.backend .cc .Symbol* sthis,
|sthis||the symbol of the current 'this' derived from fd.vthis|
|fd||the nested function|