[Sema] Make @_originallyDefinedIn a long attribute

The compiler will print the attributes on their own lines as we tend to
write them in the tests. It should make the attributes more easily readable
in the generated swiftinterfaces and such.

Author: xymus

include/swift/AST/Attr.def

@@ -534,7 +534,7 @@ SIMPLE_DECL_ATTR(IBSegueAction, IBSegueAction,
 
 DECL_ATTR(_originallyDefinedIn, OriginallyDefinedIn,
   OnNominalType | OnFunc | OnVar | OnExtension | UserInaccessible |
-  AllowMultipleAttributes |
+  AllowMultipleAttributes | LongAttribute |
   ABIBreakingToAdd | ABIBreakingToRemove | APIStableToAdd | APIStableToRemove,
   96)