www/cgihtml: set LLD_UNSAFE

This port passes an unusual option to the linker that is accepted by
ld.bfd but rejected by ld.lld. Linking with lld fails with:

ld: error: -O: number expected, but got 'string-lib.o'

PR: 226992
Approved by: portmgr (LLD_UNSAFE blanket)
Sponsored by: The FreeBSD Foundation