In D67316 we added _LIBCPP_C_HAS_NO_GETS to signal that the C library
does not provide gets(), and added a test for FreeBSD 13 or higher,
using the compiler-defined __FreeBSD__ macro.
Unfortunately this did not work that well for FreeBSD's own CI process,
since the gcc compilers used for some architectures define __FreeBSD__
to match the build host, not the target.
Instead, we should use the __FreeBSD_version macro from the userland
header <osreldate.h>, which is more fine-grained. See also