[xml] Minor patch for conditional defines in threads.c

[<Eric Zurcher csiro au>]

After struggling with git to obtain the new sources, I've just tried re-building libxml2-2.7.5 under Windows 
with the 2007 version of CodeGear ("Borland") compiler, and found one very minor problem. In threads.c, there 
are two lines reading:
#elif HAVE_WIN32_THREADS

The CodeGear compiler doesn't like this syntax for the #elif directive, but is happy with:
#elif defined(HAVE_WIN32_THREADS)

Here's a context diff:

=========================================================================================

--- a/threads.c
+++ b/threads.c
@@ -26,7 +26,7 @@
 #endif
 #ifdef HAVE_PTHREAD_H
 #include <pthread.h>
-#elif HAVE_WIN32_THREADS
+#elif defined(HAVE_WIN32_THREADS)
 #include <windows.h>
 #ifndef HAVE_COMPILER_TLS
 #include <process.h>
@@ -593,7 +593,7 @@ xmlNewGlobalState(void)
 #endif /* LIBXML_THREAD_ENABLED */
 
 #ifdef HAVE_PTHREAD_H
-#elif HAVE_WIN32_THREADS
+#elif defined(HAVE_WIN32_THREADS)
 #if !defined(HAVE_COMPILER_TLS)
 #if defined(LIBXML_STATIC) && !defined(LIBXML_STATIC_FOR_DLL)
 typedef struct _xmlGlobalStateCleanupHelperParams {

========================================================================================


Eric Zurcher
CSIRO Plant Industry
Canberra, Australia
Eric Zurcher csiro au