Fix compile errors with MacOS (#312)

* Fix compile errors with MacOS
- _POSIX_C_SOURCE must not be defined for num_CPU()

* separate util_posix.c require changes in tools directory as well

* remove unnecessary self-include

client/util_posix.h

@@ -0,0 +1,26 @@
+//-----------------------------------------------------------------------------
+// Copyright (C) 2010 iZsh <izsh at fail0verflow.com>
+//
+// This code is licensed to you under the terms of the GNU GPL, version 2 or,
+// at your option, any later version. See the LICENSE.txt file for the text of
+// the license.
+//-----------------------------------------------------------------------------
+// utilities requiring Posix library functions
+//-----------------------------------------------------------------------------
+
+#ifndef UTIL_POSIX_H__
+#define UTIL_POSIX_H__
+
+#include <stdint.h>
+
+#ifdef _WIN32
+# include <windows.h>
+# define sleep(n) Sleep(1000 *(n))
+# define msleep(n) Sleep((n))
+#else
+extern void msleep(uint32_t n);		// sleep n milliseconds
+#endif // _WIN32
+
+extern uint64_t msclock(); 			// a milliseconds clock
+
+#endif