[libxml2] Fix nanohttp.c on MinGW

[Nick Wellnhofer <nwellnhof src gnome org>]

commit d3de75782504c9136e504c6356bbae52fedf17e5
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Tue Jan 15 12:33:48 2019 +0100

    Fix nanohttp.c on MinGW
    
    Commit e3890546 broke nanohttp.c on (old) MinGW. MinGW-w64 wasn't
    affected.
    
    Should fix #36. Thanks to Simon Sobisch for the report.

 include/wsockcompat.h | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/include/wsockcompat.h b/include/wsockcompat.h
index 0484ee36..e57ca8ec 100644
--- a/include/wsockcompat.h
+++ b/include/wsockcompat.h
@@ -11,6 +11,11 @@
 #include <errno.h>
 #include <winsock2.h>
 
+/* Fix for old MinGW. */
+#ifndef _WINSOCKAPI_
+#define _WINSOCKAPI_
+#endif
+
 /* the following is a workaround a problem for 'inline' keyword in said
    header when compiled with Borland C++ 6 */
 #if defined(__BORLANDC__) && !defined(__cplusplus)