Tweak to file I/O error in file_loader.cc

Change-Id: I14fdd5ade75a34b040170249b4d2229d073b88cd
diff --git a/file_loader/file_loader.cc b/file_loader/file_loader.cc
index e6bacd2..651d9db 100644
--- a/file_loader/file_loader.cc
+++ b/file_loader/file_loader.cc
@@ -152,7 +152,8 @@
     // or exit the process. Instead these errors should be reported to the
     // caller of the FileLoader who can implement the application-specific error
     // handling policy.
-    FTL_LOG(ERROR) << "error: Unable to read Dart source '" << url << "'.";
+    std::cerr << "error: Unable to read Dart source '" << url << "'."
+              << std::endl;
     exit(1);
   }
   url_dependencies_.insert(url);