[CSSimplify] Repair should ignore situations where assignment source or destination are a hole

If either source or destination type is a hole conversion should
just be ignored because there is no r-value or other mismatch that
could be diagnosed in this case.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -5350,6 +5350,11 @@ bool ConstraintSystem::repairFailures(
       if (repairByUsingRawValueOfRawRepresentableType(lhs, rhs))
         return true;
 
+      // If either side is a placeholder then let's consider this
+      // assignment correctly typed.
+      if (lhs->isPlaceholder() || rhs->isPlaceholder())
+        return true;
+
       // Let's try to match source and destination types one more
       // time to see whether they line up, if they do - the problem is
       // related to immutability, otherwise it's a type mismatch.