swift234

Make type validation slightly more robust by caching the result.

Previously, calling type validation twice for the same type could
result in spurious errors in default arguments of tuple types. Guard
against this by recording within the ExprHandle whether the default
argument has been type-checked or not, so that it will only be done
once.

Similarly, extend the type-validation caching within TypeBase to
specify the result of type validation (succeed or fail), so that
repeated calls to validateType() will produce predictable results for
failed types.


Swift SVN r5485