$NetBSD$

Use c++20 to fix compilation errors.

--- jfbuild/kenbuild/Makefile.orig	2023-03-21 20:06:35.000000000 +0000
+++ jfbuild/kenbuild/Makefile
@@ -33,7 +33,7 @@ CXX?=g++
 RC?=windres
 
 GAMECFLAGS=-g -W -Wall -fno-strict-aliasing -std=c99
-GAMECXXFLAGS=-g -W -Wall -fno-exceptions -fno-rtti -std=c++98
+GAMECXXFLAGS=-g -W -Wall -fno-exceptions -fno-rtti -std=c++20
 GAMECPPFLAGS=-I$(SRC) -I$(ENGINEINC)
 GAMELDFLAGS=