Incorrect query of whether given comp type is an union in analyses

[pepyakin]

Analyses like derive_partial_eq_or_partial_ord assumes that if some Comp type is an union and rust target version allows us to use untagged union feature, then that Comp type will be emitted as a rust untagged union.
 
However, this can be not true, because in codegen we still can decide to emit bindgen union instead of rust union.
 
This header should reproduce the case
 

union U4 {
    unsigned derp : 1;
};