Use feature to select C++ standard

This makes the C++ standard part of the public interface.

Author: jibsen

CMakeLists.txt

@@ -12,12 +12,11 @@ endif()
 
 add_library(wideint INTERFACE wideint.hpp)
 target_include_directories(wideint INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>)
-set_target_properties(wideint PROPERTIES CXX_STANDARD 20)
+target_compile_features(wideint INTERFACE cxx_std_20)
 
 if(BUILD_TESTING)
   add_executable(test_wideint test/test_main.cpp test/test_wuint.cpp test/test_wint.cpp)
   target_link_libraries(test_wideint PRIVATE wideint)
-  set_target_properties(test_wideint PROPERTIES CXX_STANDARD 20)
 
   add_test(test_wideint test_wideint)
 endif()