Fixes #160 'missing header file on windows'

linkhash.c

@@ -21,6 +21,11 @@
 # include <endian.h>    /* attempt to define endianness */
 #endif
 
+#ifdef _MSC_VER
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>   /* Get InterlockedCompareExchange */
+#endif
+
 #include "random_seed.h"
 #include "linkhash.h"