fix databases/arangodb32 on FreeBSD 10.x

o Fix build on FreeBSD 10.x by requiring recent LLVM
o Only build on amd64 - many hardcoded directories

PR: 223815
Submitted by: galu@packetdam.com (maintainer, same as dev@dudu.ro)
Differential Revision: https://reviews.freebsd.org/D13282