build: use C++20 now that we're 5 years in and CI uses 2022+ runners.

Author: adriweb

gui/qt/CEmu.pro

@@ -60,7 +60,7 @@ TEMPLATE = app
 # Localization
 TRANSLATIONS += i18n/fr_FR.ts i18n/es_ES.ts i18n/nl_NL.ts i18n/zh_CN.ts
 
-CONFIG += c++14 c++2a c++20 console
+CONFIG += c++2a c++20 console
 
 # Seems to fix some LTO issues. See https://github.com/CE-Programming/CEmu/issues/366
 CONFIG += ltcg

gui/qt/CMakeLists.txt

@@ -48,22 +48,10 @@ set(CMAKE_SKIP_RPATH TRUE)
 set(USED_CMAKE_GENERATOR "${CMAKE_GENERATOR}" CACHE STRING "Expose CMAKE_GENERATOR" FORCE)
 message(STATUS "Detected system: ${CMAKE_SYSTEM_NAME} - host processor: ${CMAKE_HOST_SYSTEM_PROCESSOR} - CXX_COMPILER: ${CMAKE_CXX_COMPILER_ID}")
 
-# C11, and C++20 if supported otherwise C++14
 set(CMAKE_C_STANDARD 11)
 set(CMAKE_C_STANDARD_REQUIRED ON)
-include(CheckCXXCompilerFlag)
-if(MSVC)
-    CHECK_CXX_COMPILER_FLAG("/std:c++20" COMPILER_SUPPORTS_CXX20)
-else()
-    CHECK_CXX_COMPILER_FLAG("-std=c++2a" COMPILER_SUPPORTS_CXX20)
-endif()
-if(COMPILER_SUPPORTS_CXX20)
-    set(CMAKE_CXX_STANDARD 20)
-    add_definitions(-DTH_GDB_SUPPORT=1)
-else()
-    set(CMAKE_CXX_STANDARD 14)
-    set(CMAKE_CXX_STANDARD_REQUIRED ON)
-endif()
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 # Sane flags
 if(MSVC)
@@ -251,6 +239,7 @@ target_compile_definitions(CEmu PRIVATE
     CEMU_VERSION=\"${SHORT_VERSION}${VERSION_SUFFIX}\"
     DEBUG_SUPPORT
     MULTITHREAD
+    TH_GDB_SUPPORT=1
 )
 
 if(CYGWIN OR NOT WIN32)