Patch from Denis Vlasenko to add xstat() and use it.

libbb/xstat.c

@@ -0,0 +1,11 @@
+/*
+ * xstat.c - a stat() which dies on failure with meaningful error message
+ */
+#include <unistd.h>
+#include "libbb.h"
+
+void xstat(const char *name, struct stat *stat_buf)
+{
+	if (stat(name, stat_buf))
+		bb_perror_msg_and_die("Can't stat '%s'", name);
+}