math/p5-Math-Pari: set LLD_UNSAFE to avoid linking with lld

lld defaults to disallowing relocations in readonly segments (e.g., the
one containing .text). For now just fall back to linking with ld.bfd if
the system ld is lld.

PR: 214864
Approved by: portmgr (LLD_UNSAFE blanket)
Sponsored by: The FreeBSD Foundation