[libxml2] Variables need 'extern' in static lib on Cygwin

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 73b2417c5148af1f89708031b4bf96f40d1195e0
Author: Michael Haubenwallner <michael haubenwallner ssi-schaefer com>
Date:   Sat Sep 22 15:45:02 2018 +0200

    Variables need 'extern' in static lib on Cygwin
    
    While the dllimport/dllexport macros now work for Cygwin, using the
    static library still requires variables to be declared as 'extern'.
    This is a regression of c65c9e8ee07e2dab0647392c2bd1795a5bc99829,
    found+fixed by Bruno Haible using static libxml embedded in gettext.

 include/libxml/xmlexports.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/include/libxml/xmlexports.h b/include/libxml/xmlexports.h
index bc8a90d4..31ab8a10 100644
--- a/include/libxml/xmlexports.h
+++ b/include/libxml/xmlexports.h
@@ -145,7 +145,7 @@
     #if !defined(LIBXML_STATIC)
       #define XMLPUBVAR __declspec(dllimport) extern
     #else
-      #define XMLPUBVAR
+      #define XMLPUBVAR extern
     #endif
   #endif
   #define XMLCALL __cdecl