Update CMake usage to enable C++17 (#156)

The target_compile_features command allows setting PUBLIC compile features for the library, making it implicit for the applications linking it. This reduces the CMake boilerplate required to set up a dependent project (eg. ftxui-starter).

cmake/ftxui_benchmark.cmake

@@ -16,5 +16,4 @@ if (NOT WIN32)
   target_include_directories(ftxui_benchmark
     PRIVATE src
   )
-  set_property(TARGET ftxui_benchmark PROPERTY CXX_STANDARD 17)
 endif()

cmake/ftxui_set_options.cmake

@@ -10,8 +10,8 @@ function(ftxui_set_options library)
       src
   )
 
-  # C++17 is used. We requires fold expression at least.
-  set_property(TARGET ${library} PROPERTY CXX_STANDARD 17)
+  # C++17 is used. We require fold expression at least.
+  target_compile_features(${library} PUBLIC cxx_std_17)
 
   # Force Microsoft Visual Studio to decode sources files in UTF-8. This applies
   # to the library and the library users.

cmake/ftxui_test.cmake

@@ -36,7 +36,6 @@ target_include_directories(tests
 )
 target_compile_options(tests PRIVATE -fsanitize=address)
 target_link_libraries(tests PRIVATE -fsanitize=address)
-set_property(TARGET tests PROPERTY CXX_STANDARD 17)
 
 if (NOT MSVC)
   include(cmake/ftxui_benchmark.cmake)