CMake: find_package(asio) if available

if(USE_STANDALONE_ASIO)

    target_compile_definitions(simple-web-server INTERFACE ASIO_STANDALONE)

    # There is no canonical way to use Asio from CMake.

    # In particular, Asio does not support CMake natively.

    # However, Conan and Vcpkg do provide CMake support on their own.

    # Prefer the CMake target and fall back to finding asio.hpp.

    if(NOT TARGET asio::asio)

        find_package(asio)

    endif()

    if(TARGET asio::asio)

        target_link_libraries(simple-web-server INTERFACE asio::asio)

    else()

        find_path(ASIO_PATH asio.hpp)

        if(NOT ASIO_PATH)

            message(FATAL_ERROR "Standalone Asio not found")

    else()

        endif()

        target_include_directories(simple-web-server SYSTEM INTERFACE ${ASIO_PATH})

    endif()

else()