These warnings keep getting longer every homebrew release. You may want to try macPorts, which goes out of their way to explicitly support releases all the way down to 10.5.
I remember seeing SBCL builds broken on Darwin/ppc for a long while, and eventually SBCL decided to drop support for Darwin/ppc altogether. Still, these ports maintainers did not give up and eventually found a way to fix SBCL builds on PPC: https://trac.macports.org/ticket/65484
I recall seeing some work to bring back PPC support upstream, but I am not sure what the progress on that is. It's still cool seeing downstream users fix builds that simply didn't work (and to the point where upstream decides to remove support entirely since they couldn't build it anyway).
same could be said for pkgsrc I guess. I've used that on other *nix systems; haven't tried it on MacOS yet but the fact it's an option is huge
I’ve also dabbled in this area http://leopard.sh/
there are a lot of scripts out there to mitigate this but the boot-strapping is always a bit of a bother. like the script i wrote, my first instruction was "So... you go download chrome for 10.x for PPC... you can find it here in the old forgotten wasteland of google on a deserted old site that might not exist much longer... and by the way this is not secure at all"
like, you just cannot do this securely. cellularmitosis has made leopard.sh linked below, of course the first step is to download from an http site.
its kind of one of those things that have changed about the web, the cultural shock.... nowdays basically so much is based on an account, or at the very least ssl. back then nobody gave a **.
so to actually use a g5 on the modern web, like ... can you log into a video site to watch a video? well only if you dont care about being hacked when you type in your user id and password to the video site. can you shop? only if you dont care about being hacked. same.. can you browse literally anything? google will constantly harass you into logging in. so will basically everything else. and if you dont your experience will suck.
can you... write code for a g5 and try to back port modern algorithms to it? sure just log in to .. .github... on your.. insecure machine that could easily be hacked. and lose your github account to hackers. then you can cry about it after you login to social media. on your hacked account. so maybe not. then you can post about it on hacker news... where of course your account has been hacked by a keylogger.
if your machine doesnt crash because someone installed a bitcoin miner into it, or a tor node, or bittorrent or god knows what that could get you arrested.
the modern web is just such a pile of degenerate criminality and scammers and thieves and robbers, not to mention the spy agencies of various governments, that basically that is the main thing driving old systems off of it. its not that its not possible to optimize code or write new code for old platforms. its that the basic machine running an old OS is compromised at a fundamental level, open to the world for exploitation if you dare to type anything into it that is the least bit private or confidential, and its connected online.
It’s better suited for a multiuser system (and I share my desktop with my wife who has a different login) and is more stable, too.
port is the standard macOS package manager! port is the standard macOS package manager! port is the standard macOS package manager!
Then I used macports. What a nice experience. Provided what I’m after is listen on there!