Thanks to jhi and Schwern and gsar, I've got a good build of MacPerl 5.7.3, with all the extensions (except for Encode, which looks to be a lot of work to get to build), using all four compilers (MWC68K, MWCPPC, SC, MrC) and it's all committed to the new
There were very few changes to make from the 5.6.1 sources. Some updates to inheritance in MakeMaker, updated xsubpp, updated Makefile and config.h, some new symbols to take care of in makedef.pl, and a few minor things not worth mentioning. That's it.
I did make changes in File::Spec::Mac and File::Copy so they would be able to run under miniperl, as they were require'ing Mac::Files and Mac::MoreFiles. But those are changes that [cs]hould have been made for 5.6.1 anyway. So now syscopy is regular copy and rootdir returns the empty string, if those modules are unavailable.
I still need to do a few more things, including rebuilding Errno, syncing config.sh (yes, it is a separate job from syncing config.sh), and, last but last, running all the tests (which will likely include another change to MacPerl's use of Unix paths in require/use/lib). Hopefully this will not uncover a big batch of things that need to be fixed.
After I get this well underway, I will get back to MacPerl 5.6.1r2, a bugfix release. That's been pushed back a few weeks so I could work on 5.8, but I don't think anyone is going to be complaining much.