handle unbound vars in NTuple fields (#55405)

Comparing objects by `==` will happily answer nonsense for malformed
type comparisons, such as `unwrap_unionall(A) == A`. Avoid forming that
query. Additionally, need to recourse through Vararg when examining type
structure to make decisions.

Fix #55076
Fix #55189

(cherry picked from commit 32423a8)

Author: vtjnash

src/builtins.c

@@ -1715,6 +1715,12 @@ static int references_name(jl_value_t *p, jl_typename_t *name, int affects_layou
         return references_name(((jl_uniontype_t*)p)->a, name, affects_layout, freevars) ||
                references_name(((jl_uniontype_t*)p)->b, name, affects_layout, freevars);
     }
+    if (jl_is_vararg(p)) {
+        jl_value_t *T = ((jl_vararg_t*)p)->T;
+        jl_value_t *N = ((jl_vararg_t*)p)->N;
+        return (T && references_name(T, name, affects_layout, freevars)) ||
+               (N && references_name(N, name, affects_layout, freevars));
+    }
     if (jl_is_typevar(p))
         return 0; // already checked by unionall, if applicable
     if (jl_is_datatype(p)) {