Switch to c++ 23 standard (#1985)

CMakeLists.txt

@@ -2,6 +2,10 @@ cmake_minimum_required(VERSION 3.27)
 cmake_policy(SET CMP0060 OLD) #causes link errors on Linux otherwise
 cmake_policy(SET CMP0065 OLD) #we need binaries compiled with -rdynamic for BARb to work (cause unknown https://github.com/beyond-all-reason/spring/issues/405)
 
+set(CMAKE_CXX_STANDARD 23)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
 set(CMAKE_MODULES_SPRING "${CMAKE_CURRENT_SOURCE_DIR}/rts/build/cmake")
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_MODULES_SPRING}")
 
@@ -362,13 +366,6 @@ else  (LDGOLD_FOUND)
 	message(WARNING "You are using ld.bfd, it's much slower than ld.gold.")
 endif (LDGOLD_FOUND)
 
-message(STATUS "Compiling with C++20")
-if(MSVC)
-	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++20 /permissive- /Zc:__cplusplus")
-else (MSVC)
-	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++20")
-endif(MSVC)
-
 add_definitions(-D_GLIBCXX_USE_NANOSLEEP) # issue in std::chrono with gentoo and few other distros
 
 

rts/Rendering/Fonts/ustring.h

@@ -4,10 +4,6 @@
 
 #include <string>
 
-#if __cplusplus < 202002L
-	using char8_t = unsigned char;
-#endif
-
 namespace spring {
 	class u8string : public std::string {
 	public: