MSVC port (vardyh) (#746)

* unicorn: use waitable timer to implement usleep() on Windows

Signed-off-by: vardyh <vardyh.dev@gmail.com>

* atomic: implement barrier() for msvc

Signed-off-by: vardyh <vardyh.dev@gmail.com>

qemu/include/qemu/atomic.h

@@ -19,8 +19,9 @@
 
 /* Compiler barrier */
 #ifdef _MSC_VER
-// TODO: fix me!!!
-#define barrier()   //{ __asm volatile("" ::: "memory"); (void)0; }
+void _ReadWriteBarrier(void);
+#pragma intrinsic(_ReadWriteBarrier)
+#define barrier()   do { _ReadWriteBarrier(); } while (0)
 #else
 #define barrier()   ({ asm volatile("" ::: "memory"); (void)0; })
 #endif