Cleanup build_sdk error checking

pkg/dev_compiler/tool/build_sdk.dart

Index: pkg/dev_compiler/tool/build_sdk.dart
diff --git a/pkg/dev_compiler/tool/build_sdk.dart b/pkg/dev_compiler/tool/build_sdk.dart
index 91812eec3b212641adbe1eb33d12f2e770742bed..9761f1ddbe027b413ce8375ee424f881d9c833fe 100644
--- a/pkg/dev_compiler/tool/build_sdk.dart
+++ b/pkg/dev_compiler/tool/build_sdk.dart
@@ -9,6 +9,8 @@
 /// command line interface. But being able to build from a Dart library means
 /// we can call this during code coverage to get more realistic numbers.
 
+import 'dart:io';
+
 import 'package:dev_compiler/src/compiler/command.dart';
 
 main(List<String> arguments) {
@@ -52,7 +54,6 @@ main(List<String> arguments) {
     'dart:web_sql'
   ]);
 
-  if (compile(args) != 0) {
-    throw 'SDK build failed.';
-  }
+  var result = compile(args);
+  exit(result);
 }