fix missing effects specifiers on eff props in swiftinterface

I missed the case where the body is also being printed in the
interface file.

lib/AST/ASTPrinter.cpp

@@ -3490,6 +3490,10 @@ void PrintAST::visitAccessorDecl(AccessorDecl *decl) {
       });
   }
 
+  // handle effects specifiers before the body
+  if (decl->hasAsync()) Printer << " async";
+  if (decl->hasThrows()) Printer << " throws";
+
   printBodyIfNecessary(decl);
 }