LLVM 3.5 is overdue to removal and lang/pure is one of two ports that depend on it.
I currently don't have time and motivation to look into it. However, I noticed that the official port in Arch linux's AUR (https://aur.archlinux.org/packages/?SeB=m&K=pure-aur&PP=100) also uses LLVM35 :/
(In reply to Brooks Davis from comment #0)
Already documented in https://wiki.freebsd.org/ObsoleteLLVMVersions .
Here's the upstream issue, FWIW:
A commit references this bug:
Date: Wed Mar 20 23:18:50 UTC 2019
New revision: 496395
Set an expiration date somewhat after the 5th anniversary of this port's
creation. It has been effectivly unmaintained upstream for 4.5 years at
PR: 230473, 230475
See also ports r503721.
Expired port removed.