Log Message:
Any package that determines libraries to link via:

  $PYTHON -c "from distutils import sysconfig; print \ 
sysconfig.get_config_var('SHLIBS');"

... where bdb.buildlink.mk has been used and it satisfied the requirement from
Pkgsrc (E.g. via databases/db4) would fail to build because the required -ldb4
library was not itself buildlinked.

To rectify this, pull in bdb.buildlink.mk in python??/buildlink3.mk under the
same conditions as it is pulled in in the package's own makefile.

No revision bump required, this almost certainly only affects packages and
environments that simply wouldn't build at all prior to the fix.

Fixes the build of py-ORBit on Linux (Python 2.4 or 2.5), and PR39377.