Merge remote-tracking branch 'origin/swift-3.0-branch' into stable
* origin/swift-3.0-branch:
Fix bug in using shadow decl checking: a using shadow decl should not conflict with a prior UsingDecl -- those should not even really be found by the lookup here, except that we use the same lookup results for two different checks, and the other check needs them.
Twek fix for PR24473 (r261506) - Preserve the template arguments as written (within the DeclRefExpr Node) when creating AST nodes that reference specializations of static data member templates. While we pass the template args through for all non-instance members, they should only be relevant (i.e. non-null) for variable template ids (assertion added for that assumption)
PR26237: Fix iterator invalidation bug that occurs if serializing specializations of a template manages to trigger deserialization of more specializations of the same template.
Amends r252104 to evaluate the controlling expression in an unevaluated context. This eliminates false-positive diagnostics about null pointer dereferences (etc) in the controlling expression.
