[libc++] Add FreeBSD XFAILs in preparation for CI

This at least allows us to stand up libc++ FreeBSD CI and avoid future
regressions.  The failures do need to be addressed, and can be done
iteratively.

Reviewed By: philnik, Mordante

Differential Revision: https://reviews.llvm.org/D141542

NOKEYCHECK=True
GitOrigin-RevId: 7ec6c629052c30c0772e8fcae346a405af43444e
1 file changed