Log the pid of the forked zygote child.

Useful to link together the pids of the zygote and its children in logcat
output.

Test: Flash and boot, run "adb logcat"
Change-Id: I524b70aed7d1ce7a378df0e2b2063e23f1f9a454

core/jni/com_android_internal_os_Zygote.cpp

@@ -892,6 +892,8 @@ static pid_t ForkCommon(JNIEnv* env, bool is_system_server,
 
     // Turn fdsan back on.
     android_fdsan_set_error_level(fdsan_error_level);
+  } else {
+    ALOGD("Forked child process %d", pid);
   }
 
   // We blocked SIGCHLD prior to a fork, we unblock it here.