Old compilers (example: gcc < 7, mingw or VS older than 2022) don't
work with latest croaring versions; note that we had this issue even
before this change...
We somehow try to autodect if we can use latest version (TODO: we can do
better!): otherwise we fallback to legacy code.
The user can force that via `--enable-old-croaring` option: that's the
option to use if you get any errors on `roaring.c` filw while compiling.
Remove `-AC_COMPILE_IFELSE` check which does nothing and provides
misleading output!
On CI, we always use legacy version on Windows (if we use VisualStudio)
and with Mingw compiler.
Please, note that before the recent code adding
`NDPI_UNRESOLVED_HOSTNAME` support, the croaring code, even if present
in the repository, was NEVER used!!
