Well done!
There is some infection point between the wx3.11 and wx3.12 where it stops working on G4/G5. I have a build on my G5 iMac that works. I'll post it up when I get a chance. Newer versions than that commit hash won't build, but it's compatible enough. I suppose wx3.0.4 should build fine too.
I'll probably do a dual release for the release version of 1.2.7 where it's a fat binary for classic macs that supports 10.4 PPC-32, 10.5 PPC-64, 10.5 i386 and then a more modern 10.11+ for just x86_32|64.
I've got a 10.11 El Capitan Vbox VM that mostly works well enough to build on.
My old 2009 core2 intel 15" mbp w/10.9.5 doesn't seem to be able to build proper binaries and the lldb debugger is terrible there as backtrace and list don't work too well to track down bugs, not sure why. Binaries built on that box all crash.
But binaries built on 10.11VM do work on 10.12, and 10.14 and 10.15 VMs, and on 10.11, clang + lldb work pretty well and I can debug most things, it's just that the display isn't GPU accelerated so I can't tell how well it would do on real hardware, though I do have a 10.14 on a fairly recent Mac that works well.
I wish I could get a working build for as low as 10.7 as supposedly wxWidgets 3.x does go that low. But... it is what it is.
I'll likely test it on FreeBSD, and OpenIndiana (and maybe OpenBSD) as well before the final 1.2.7 release (or maybe I'll leave that for 1.2.8 ), but I don't expect too many issues with those OSs. I tried to get the latest Oracle Solaris 11.4 in a VM, but it's quite crashy, so not going to bother with that. Might be nice to get it working on AIX 4 or 5 as well, but that would be more of a curiosity than anything anyone would likely care about (assuming I can even get wx to compile on those beasts)
Anyway, I've just rewritten the build system using the scripts from 1.3.0 which use a file system layout where the directories are organized like the Lisa's hardware - that was the original intent from the very first versions in 1998, but once I got to ~2007 I gave that up. So bringing it back now. So what's gonna happen next is that the 1.2.x repo on github will go into deprecated mode and I'll have a new repo called just "lisaem" without the lame ass version number. I was saving that for when 1.3.0 was working, but, I can do that in a few days once this stuff is stable.
But more urgently, I gotta write the Cygwin scripts for building on windows. I'm using this VM for that:
https://developer.microsoft.com/en-us/windows/downloads/virtual-machines so I have to finish that bit before the end of the month or it will expire.
They're usually pretty good about releasing new versions a couple of weeks after they expire, but who knows when they'll end that program. Unfortunately on the pre-built windows versions, the wx-config command doesn't exist, so I'll have to deduce the wx-config --libs and --cflags and --cxxflags outputs from Linux and macos and deal with a bunch of cygpath translations to make shit work right. Originally I relied on wxdsgn off sourceforge, but that's been abandoned ~2011 or so. Too bad, as it was a nice IDE and had pre-built wxWidgets for Windows.
I did manage to script a couple of batch files that do an unattended Cygwin install with the mingw32/64 compilers, so there's that at least.