Use _WIN32 rather than HAVE_WINSOCK.

Change-Id: I9855b6fe72e2f2f3a8360c0993a67cb988024ee4
diff --git a/libutils/Unicode.cpp b/libutils/Unicode.cpp
index fb876c9..6f4b721 100644
--- a/libutils/Unicode.cpp
+++ b/libutils/Unicode.cpp
@@ -18,7 +18,7 @@
 
 #include <stddef.h>
 
-#ifdef HAVE_WINSOCK
+#if defined(_WIN32)
 # undef  nhtol
 # undef  htonl
 # undef  nhtos