The rpath is definitely needed, but I have no idea what problem Solaris ld has here.
Look closely: There is a "-Wl,-R" preceding the "-Wl,-rpath" from your patch, which in turn is followed by the path. So ld sees "-R -rpath /usr/pkgsrc/...". This is not a problem of the linker. Maybe it's autoconf.
-- Jörn Clausen joern.clausen%uni-bielefeld.de@localhost Hochschulrechenzentrum http://www.uni-bielefeld.de/hrz/ Universität Bielefeld