Fix windows libobjc build (PR libobjc/93099)

2020-01-01  Andrew Pinski  <pinskia@gmail.com>

        PR libobjc/93099
        * objc/objc-decls.h (objc_EXPORT): Define it to
        extern for DLL_EXPORT define case.

From-SVN: r279822

libobjc/ChangeLog

+2020-01-01  Andrew Pinski  <pinskia@gmail.com>
+
+	PR libobjc/93099
+	* objc/objc-decls.h (objc_EXPORT): Define it to
+	extern for DLL_EXPORT define case.
+
 2020-01-01  Jakub Jelinek  <jakub@redhat.com>
 
 	Update copyright years.

libobjc/objc/objc-decls.h

@@ -29,7 +29,7 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #if defined (_WIN32) || defined (__WIN32__) || defined (WIN32)
 
 #  ifdef DLL_EXPORT /* defined by libtool (if required) */
-#    define objc_EXPORT 
+#    define objc_EXPORT extern
 #    define objc_DECLARE
 #  else
 #    define objc_EXPORT  extern __declspec(dllimport)