This changes the buildlink3.mk files to use an include guard for the
recursive include. The use of BUILDLINK_DEPTH, BUILDLINK_DEPENDS,
BUILDLINK_PACKAGES and BUILDLINK_ORDER is handled by a single new
variable BUILDLINK_TREE. Each buildlink3.mk file adds a pair of
enter/exit marker, which can be used to reconstruct the tree and
to determine first level includes. Avoiding := for large variables
(BUILDLINK_ORDER) speeds up parse time as += has linear complexity.
The include guard reduces system time by avoiding reading files over and
over again. For complex packages this reduces both %user and %sys time to
half of the former time.
This is a newer version of what we have as pkgsrc/print/pdflib, but
it comes with much unfriendlier licensing conditions (non-commercial
use only).
I've tested it with gnuplot. There is just some "dash patterns" support
added over pdflib4 afaics. So making it the default choice isn't worth
the hassle, but if you want to try it, here is it.
