AU: Pass opened device fd from update engine to bspatch.

subprocess.h

Index: subprocess.h
diff --git a/subprocess.h b/subprocess.h
index 8f97c5d2b8be5a8938b946908e7d66fe2c80edac..bf1e7ea7ca4cfe3b17628236be8b9e04d4c2f0a6 100644
--- a/subprocess.h
+++ b/subprocess.h
@@ -37,8 +37,13 @@ class Subprocess {
   void CancelExec(uint32_t tag);
 
   // Executes a command synchronously. Returns true on success.
+  static bool SynchronousExecFlags(const std::vector<std::string>& cmd,
+                                   int* return_code,
+                                   GSpawnFlags flags);
   static bool SynchronousExec(const std::vector<std::string>& cmd,
-                              int* return_code);
+                              int* return_code) {
+    return SynchronousExecFlags(cmd, return_code, static_cast<GSpawnFlags>(0));
+  }
 
   // Gets the one instance
   static Subprocess& Get() {