add missing file

libbb/xvfork.c

@@ -0,0 +1,18 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Utility routines.
+ *
+ * Copyright (C) 2007 Denys Vlasenko
+ *
+ * Licensed under GPL version 2, see file LICENSE in this tarball for details.
+ */
+
+#include "libbb.h"
+
+pid_t FAST_FUNC xvfork(void)
+{
+	pid_t pid = vfork();
+	if (pid < 0)
+		bb_perror_msg_and_die("vfork");
+	return pid;
+}