vpnor: Shuffle and rework includes for sanity

Include ordering and whether or not C linkage is forced by `extern "C"`
blocks can cause headaches at link time. Ensure that all C dependencies
are included in an `extern C` block before other includes occur. Also
include the C++ versions of string.h and assert.h

Change-Id: Ia96f6044d40c8eccb907b65924efcf62ac7a89c3
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/vpnor/test/tmpd.hpp b/vpnor/test/tmpd.hpp
index 2239f9c..7386f2f 100644
--- a/vpnor/test/tmpd.hpp
+++ b/vpnor/test/tmpd.hpp
@@ -3,17 +3,18 @@
 
 #include "config.h"
 
+extern "C" {
+#include "mboxd.h"
+}
+
 #include "vpnor/pnor_partition_table.hpp"
 
-#include <assert.h>
-#include <string.h>
-
+#include <cassert>
+#include <cstring>
 #include <experimental/filesystem>
 #include <fstream>
 #include <vector>
 
-#include "mboxd.h"
-
 namespace openpower
 {
 namespace virtual_pnor