Define SIZEOF_LONG_LONG for Windows.

This is important not only for consistency with the other platforms but also
because without SIZEOF_LONG_LONG being defined, "%lu" format specifier can't
be used with size_t values under Win64, as Arg_Size_t is not defined correctly
there if SIZEOF_LONG_LONG is unknown.

Closes #15670.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75206 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/defs.h

@@ -953,6 +953,10 @@ typedef wxUint16 wxWord;
             #define SIZEOF_LONG 4
         #endif
 
+        #ifndef SIZEOF_LONG_LONG
+            #define SIZEOF_LONG_LONG 8
+        #endif
+
         #ifndef SIZEOF_WCHAR_T
             /* Windows uses UTF-16 */
             #define SIZEOF_WCHAR_T 2