I see a potential for version skew with the current buildlink.mk system.

If you build a program P which depends on installed library L, then
L/buildlink.mk is used.

But this version of L/buildlink.mk is the version for the most recent
version in pkgsrc. Program P may not require the most recent version but
may be happy with an older version that was installed earlier.

In this case, the L/buildlink.mk does not belong to the installed
version of L. To make sure that this can never be a problem, we must
install L/buildlink.mk with L, so that when linking with L the
buildlink.mk from that time is used.

Alternatively, each buildlink.mk needs to be backward-compatible to
*all* possibly previously installed versions.

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert - rhialto@polder --They that can give up essential 
\X/ land.nl --liberty to purchase a little temporary safety
--------------deserve neither liberty or safety. - Benjamin Franklin, 1759
---People will accept your ideas much more readily if you tell them that
---Benjamin Franklin said it first. - Unknown