cmake LIBURINGCXX_HAS_KERNEL_RWF_T examples

Codesire-Deng/co_context extern/liburingcxx/cmake/configure.cmake :12

check_cxx_source_runs(
    [====[
    #include <linux/fs.h>
    int main(int argc, char **argv)
    {
      __kernel_rwf_t x;
      x = 0;
      return x;
    }
    ]====]
    LIBURINGCXX_HAS_KERNEL_RWF_T
)