cmake_minimum_required(VERSION 3.18)
project(test)

add_executable(test
    main.cxx
    test.c
)

target_compile_options(test PRIVATE
    $<$<COMPILE_LANGUAGE:CXX>:-std=c++11>
    $<$<COMPILE_LANGUAGE:C>:-std=gnu99>
)

file(GENERATE OUTPUT summary.txt
    CONTENT $<TARGET_PROPERTY:test,COMPILE_OPTIONS>
)


[cmake] CMake Error in CMakeLists.txt:
[cmake]   Evaluation file to be written multiple times with different content.  This
[cmake]   is generally caused by the content evaluating the configuration type,
[cmake]   language, or location of object files:
[cmake]
[cmake]    C:/projects/tasks/cmake-cxx-flags/build/debug/summary.txt