Fix using right functions for file descriptor with MS Visual Studio

tls/compat/getuid.c

@@ -4,6 +4,8 @@
  * Kinichiro Inoguchi <inoguchi@openbsd.org>
  */
 
+#ifdef _WIN32
+
 #include <unistd.h>
 
 uid_t
@@ -12,3 +14,5 @@ getuid(void)
 	/* Windows fstat sets 0 as st_uid */
 	return 0;
 }
+
+#endif