[Rpcemu] NX/XD/DEP patch

I've added support for DEP on Windows and re-done the 'length' calculation for Linux (mprotect) as it looked wrong to me (potentially including one too few or one too many pages if I'm not mistaken). I've only tested it on a Windows10/64-bit host however.

Not sure if the mailing list can handle file attachments so I'll just copy/paste the diff:

diff -r b0e396f600d9 src/codegen_amd64.c
--- a/src/codegen_amd64.c    Sat May 05 21:00:45 2018 +0100
+++ b/src/codegen_amd64.c    Sun May 13 23:20:07 2018 +0100
@@ -32,11 +32,7 @@
 #include "mem.h"
 #include "arm.h"
 #include "arm_common.h"
-
-#if defined __linux__ || defined __MACH__
-#include <sys/mman.h>
-#include <unistd.h>
-