Cange c++std from c++20 to gcc specific c++2a to reduce the required gcc version

CMakeLists.txt

@@ -57,7 +57,7 @@ endif(WIN32)
 add_library(${PROJECT_NAME} SHARED ${SRC_FILES})
 target_link_libraries(${PROJECT_NAME} ${LIBS})
 target_include_directories(${PROJECT_NAME} PUBLIC eisgenerator)
-set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS "-std=c++20 -Wall -O2 -march=native -g" LINK_FLAGS "-flto")
+set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS "-std=c++2a -Wall -O2 -march=native -g" LINK_FLAGS "-flto")
 
 set(CMAKE_INSTALL_PREFIX "/usr")
 install(TARGETS ${PROJECT_NAME} DESTINATION lib)
@@ -73,7 +73,7 @@ add_executable(${PROJECT_NAME}_test ${SRC_FILES_TEST_APP})
 add_dependencies(${PROJECT_NAME}_test ${PROJECT_NAME})
 target_link_libraries(${PROJECT_NAME}_test ${LIBS_TEST})
 target_include_directories(${PROJECT_NAME}_test PUBLIC eisgenerator)
-set_target_properties(${PROJECT_NAME}_test PROPERTIES COMPILE_FLAGS "-std=c++20 -Wall -O2 -march=native -g" LINK_FLAGS "-flto")
+set_target_properties(${PROJECT_NAME}_test PROPERTIES COMPILE_FLAGS "-std=c++2a -Wall -O2 -march=native -g" LINK_FLAGS "-flto")
 install(TARGETS ${PROJECT_NAME}_test DESTINATION bin)
 
 link_directories(${CMAKE_CURRENT_BINARY_DIR})
@@ -83,5 +83,5 @@ add_executable(${PROJECT_NAME}_export ${SRC_FILES_TEST_APP})
 add_dependencies(${PROJECT_NAME}_export ${PROJECT_NAME})
 target_link_libraries(${PROJECT_NAME}_export ${LIBS_TEST})
 target_include_directories(${PROJECT_NAME}_export PUBLIC eisgenerator)
-set_target_properties(${PROJECT_NAME}_export PROPERTIES COMPILE_FLAGS "-std=c++20 -Wall -O2 -march=native -g" LINK_FLAGS "-flto")
+set_target_properties(${PROJECT_NAME}_export PROPERTIES COMPILE_FLAGS "-std=c++2a -Wall -O2 -march=native -g" LINK_FLAGS "-flto")
 install(TARGETS ${PROJECT_NAME}_export DESTINATION bin)