Fix patch file return types

sdk/lib/io/process.dart

Index: sdk/lib/io/process.dart
diff --git a/sdk/lib/io/process.dart b/sdk/lib/io/process.dart
index fd61c56e5145ab8c4a279962bd10b59df84e8fd5..c1a060a556ffdba90ab40e2047814ff809df194a 100644
--- a/sdk/lib/io/process.dart
+++ b/sdk/lib/io/process.dart
@@ -7,9 +7,9 @@ part of dart.io;
 // TODO(ager): The only reason for this class is that we
 // cannot patch a top-level at this point.
 class _ProcessUtils {
-  external static _exit(int status);
-  external static _setExitCode(int status);
-  external static _sleep(int millis);
+  external static void _exit(int status);
+  external static void _setExitCode(int status);
+  external static void _sleep(int millis);
   external static int _pid(Process process);
 }