Remove ::gets for FreeBSD 13 and later

In @emaste removed gets() from
FreeBSD 13's libc, and our copies of libc++ and libstdc++.  In that change, the
declarations were simply deleted, but I would like to propose this conditional
test instead.

Reviewers: EricWF, mclow.lists, emaste

Reviewed By: mclow.lists

Subscribers: krytarowski, christof, ldionne, emaste, libcxx-commits

Differential Revision:

git-svn-id: 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed