[Constraint solver] Check labels of unresolved member references.

We don’t really allow overloading of case names based on labels, so we can’t
really test this, but we’re supposed to so I’ll fix the code ;)

Author: DougGregor

lib/Sema/CSSimplify.cpp

@@ -131,6 +131,8 @@ bool constraints::areConservativelyCompatibleArgumentLabels(
     hasCurriedSelf = false;
   } else if (baseType->is<AnyMetatypeType>() && decl->isInstanceMember()) {
     hasCurriedSelf = false;
+  } else if (isa<EnumElementDecl>(decl)) {
+    hasCurriedSelf = false;
   } else {
     hasCurriedSelf = true;
   }
@@ -142,6 +144,8 @@ bool constraints::areConservativelyCompatibleArgumentLabels(
   } else if (auto subscript = dyn_cast<SubscriptDecl>(decl)) {
     assert(!hasCurriedSelf && "Subscripts never have curried 'self'");
     fTy = subscript->getInterfaceType()->castTo<AnyFunctionType>();
+  } else if (auto enumElement = dyn_cast<EnumElementDecl>(decl)) {
+    fTy = enumElement->getInterfaceType()->castTo<AnyFunctionType>();
   } else {
     return true;
   }