fix: some compiler warning when the #define is not matching.

client/sleep.c

@@ -8,7 +8,7 @@
 // platform-independant sleep macros
 //-----------------------------------------------------------------------------
 
-#ifndef _WIN32
+#ifndef __WIN32
 
 #define _POSIX_C_SOURCE	199309L
 #include "sleep.h"
@@ -24,5 +24,4 @@ void nsleep(uint64_t n) {
   while (nanosleep(&timeout, &timeout) && errno == EINTR);
 }
 
-#endif // _WIN32
-
+#endif // _WIN32