Start the implementation of a "nocapture" attribute, which is only valid on paramdecls.

This is part of rdar://16323038.  Because this hasn't been fully design reviewed and
implemented, I'm naming it as __nocapture for now.  It is blocking finishing off the
"improved let model" work.




Swift SVN r24079

lib/Serialization/Serialization.cpp

@@ -2380,7 +2380,8 @@ void Serializer::writeType(Type ty) {
            fnTy->isAutoClosure(),
            fnTy->getRepresentation() == AnyFunctionType::Representation::Thin,
            fnTy->isNoReturn(),
-           fnTy->getRepresentation() == AnyFunctionType::Representation::Block);
+           fnTy->getRepresentation() == AnyFunctionType::Representation::Block,
+                                   fnTy->isNoCapture());
     break;
   }