I am trying to make some packages that need to rely on the make
variable BUILDLINK_PREFIX.<pkg>.  For example, one depends on
x11/qt3-libs and needs the value of $QTDIR (which is set in
x11/qt3-libs/buildlink3.mk).  The file mk/buildlink3/bsd.buildlink3.mk
includes the following:

# Note that if a buildlink3.mk file is included, then the package Makefile
# has the expectation that it can use the value of BUILDLINK_PREFIX.<pkg>.
# If the buildlink3.mk tries to handle dependencies satisfied directly by
# the base system, then it should provide an appropriate value for
# BUILDLINK_PREFIX.<pkg> for that case.  The case where a dependency is
# satisfied by a pkgsrc-installed package is handled automatically by this
# file.

This implies to me that the following commands should produce
something useful (in a package that includes
x11/qt3-libs/buildlink3.mk):

	make show-var VARNAME=BUILDLINK_PREFIX.qt3
	make show-var VARNAME=QTDIR

However, with the 2006Q2 version of pkgsrc, both commands produce
blank lines.  So does the command

	cd devel/bison && make show-var VARNAME=BUILDLINK_PREFIX.gettext-lib

which suggests that this does not depend on something specific to my
package.

I must be missing something or misunderstanding the use of
$BUILDLINK_PREFIX.<pkg> or 'make show-var'.  Any help is greatly
appreciated.

Cheers,
Brook