I've managed to build bebbo's toolchain, so I'll give that a try. Thanks very much.
Re not being able to distribute modifications: it means I can't check the source code into my VCS, edit the Makefile to preconfigure it, add a file to make it build with my non-Make-based build system, or fix any bugs. I'd have to distribute the original source archive, and add machinery to my build system to unpack it and apply an external patch in order to build it. And it still wouldn't be allowed in Debian.
I've actually done this before with vbcc (see
https://cowlark.com/vbcc-z-compiler) and it just isn't worth it, especially if I can find a different toolchain.