Fix two semantic errors from my previous check-in.

runtime/bin/builtin_natives.cc

Index: runtime/bin/builtin_natives.cc
diff --git a/runtime/bin/builtin_natives.cc b/runtime/bin/builtin_natives.cc
index 214bd28db1c0de5430f0cc57d3c215b24a517675..eadd3296886852f8086ee33395396f9fd1981b28 100644
--- a/runtime/bin/builtin_natives.cc
+++ b/runtime/bin/builtin_natives.cc
@@ -112,7 +112,7 @@ void Builtin::PrintString(FILE* out, Dart_Handle str) {
     // an isolate gets interrupted by the embedder in the middle of
     // Dart_StringToBytes?  We need to make sure not to swallow the
     // interrupt.
-    fputs(Dart_GetError(result));
+    fputs(Dart_GetError(result), out);
   } else {
     fwrite(characters, sizeof(*characters), length, out);
   }