||Differentiate between tuple and struct types for Rust
Section 5.7, pg 113
Rust has two different structure types -- tuples and structs.
(Actually it also has tuple structs, but those can be handled like tuples.)
Structs have field names, while tuples use numbers.
Currently, DWARF readers use the member names to differentiate between the two.
However, there are empty variants of both tuples and structs, and these
can't be distinguished without some additional help.
Perhaps adding DW_TAG_tuple_type would be worthwhile here.