re PR libstdc++/89824 (Variant jump table reserves space for __variant_cookie twice)

PR libstdc++/89824

Fix based on a suggestion by Antony Polukhin.
* include/std/variant (__gen_vtable): Don't reserve an
additional table slot, _Multi_array already does that.

From-SVN: r269941

libstdc++-v3/ChangeLog

 2019-03-26  Ville Voutilainen  <ville.voutilainen@gmail.com>
 
+	PR libstdc++/89824
+	Fix based on a suggestion by Antony Polukhin.
+	* include/std/variant (__gen_vtable): Don't reserve an
+	additional table slot, _Multi_array already does that.
+
+2019-03-26  Ville Voutilainen  <ville.voutilainen@gmail.com>
+
 	PR libstdc++/89816
 	Fix based on a suggestion by Antony Polukhin.
 	* include/std/variant (__variant_construct): Capture a pointer

libstdc++-v3/include/std/variant

@@ -904,9 +904,7 @@ namespace __variant
       using _Func_ptr = _Result_type (*)(_Visitor&&, _Variants...);
       using _Array_type =
 	  _Multi_array<_Func_ptr,
-		       (variant_size_v<remove_reference_t<_Variants>>
-			+ (is_same_v<_Result_type, __variant_cookie> ? 1 : 0))
-	               ...>;
+		       variant_size_v<remove_reference_t<_Variants>>...>;
 
       static constexpr _Array_type
       _S_apply()