Thanks to the bsd-port-dev mailing list for removing some cryft from the build process.
One important thing is that the latest repo seems to now be broken with SoyLatte. Bootstrapping with an earlier OpenJDK 7 (eg the ones on Landon Fuller's page: http://landonf.bikemonkey.org/code/java/OpenJDK_7_Binaries.20080820.html) now seems to be essential.
The current repo is now working on Mac OS X again, providing that you apply the patches provided by Michael Franz (see: http://mail.openjdk.java.net/pipermail/bsd-port-dev/2008-December/000189.html for the post, the attachment with the patch is: http://mail.openjdk.java.net/pipermail/bsd-port-dev/attachments/20081213/9b7550d6/attachment-0001.obj )
It still fails over the "Queens.java" issue mentioned by Karen Kinnear (http://mail.openjdk.java.net/pipermail/bsd-port-dev/2008-September/000044.html) - to work around this, find sources/hotspot/make/bsd/makefiles/buildtree.make and edit it, so that the test_gamma target is simply:
(ie, so that test_gamma is now an empty target). The build will still fail, complaining that:
build/bsd-i586/hotspot/outputdir/bsd_i486_compiler2/product/test_gamma does not exist.
Create this as an empty file, with executable permission and rerun the make command. It will pick up where it left off and then fail because:
build/bsd-i586/hotspot/outputdir/bsd_i486_compiler1/product/test_gamma does not exist.
These are, presumably the server and client JVMs respectively. Repeat the fix, creating an empty test_gamma in the compiler1 tree, and all should be well.
This JVM should be saved somewhere (/usr/local seems like a good place) and can be used for testing. I've rerun the build using a JDK generated like this, and it seems happy.
(Btw, patches for the above build process, especially that ungainly test_gamma hack, would be very welcome).