BUILDLINK_PASSTHRU_RPATHDIRS documentation

[Mayuresh <mayuresh%acm.org@localhost>]

I have a scenario. Package p1 installs a library at a location other than
$PREFIX/lib. Package p2 links with it and wants to embed its path in the
RPATH.

What is an idiomatic way to deal with this? Saw some packages making use
of BUILDLINK_PASSTHRU_RPATHDIRS and it worked for me. But is that the
solution for above scenario or is there something else?

make help or pkgsrc.txt currently do not document
BUILDLINK_PASSTHRU_RPATHDIRS

A quick grep shows, very few packages seems to be using this. I'd imagine
above scenario may not be so uncommon. So wonder if there is some other
way to handle it.

-- 
Mayuresh