[CSBindings] Make sure that transitive bindings aren't inferred on itself

It's possible to find current type variable while trying to infer
transitive bindings (because sources are gathered from multiple
different type variables and current type variable could be a
representative of an equivalence class), let's make sure we don't
attempt to use constraints which refer to current type variable
on the left-hand side.

Resolves: rdar://problem/65724310

Author: xedin

lib/Sema/CSBindings.cpp

@@ -47,7 +47,7 @@ void ConstraintSystem::PotentialBindings::inferTransitiveBindings(
   for (auto *constraint : conversions) {
     auto *tv =
         cs.simplifyType(constraint->getFirstType())->getAs<TypeVariableType>();
-    if (!tv)
+    if (!tv || tv == TypeVar)
       continue;
 
     auto relatedBindings = inferredBindings.find(tv);