[gtk/gtk-3-24: 1/2] Add a missing 'extern' attribute, to fix building with -fno-common

[Matthias Clasen <matthiasc src gnome org>]

commit 01d4c29ce34d534110cd67cc5af5b3884750423e
Author: Martin Storsjö <martin martin st>
Date:   Sun Apr 5 00:26:19 2020 +0300

    Add a missing 'extern' attribute, to fix building with -fno-common
    
    With C compilers defaulting to -fcommon, this isn't an issue, but
    upcoming compilers (GCC 10 and Clang 11) will default to -fno-common,
    ending up with duplicate definitions of this variable.

 gdk/win32/gdkprivate-win32.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gdk/win32/gdkprivate-win32.h b/gdk/win32/gdkprivate-win32.h
index e8ca08ce14..99616e170d 100644
--- a/gdk/win32/gdkprivate-win32.h
+++ b/gdk/win32/gdkprivate-win32.h
@@ -298,7 +298,7 @@ extern UINT          _gdk_input_codepage;
 extern guint            _gdk_keymap_serial;
 
 /* The singleton selection object pointer */
-GdkWin32Selection *_win32_selection;
+extern GdkWin32Selection *_win32_selection;
 
 void _gdk_win32_dnd_do_dragdrop (void);
 void _gdk_win32_ole2_dnd_property_change (GdkAtom       type,