Hello,
Unfortunately, no update since 17 january (that was one week ago!)
I don't have more information on how Unity is progressing on this, but feel free to ask them on their forum and post here if you have more info.
About your idea, I already thought about something like that, but the problem is that the Unity il2cpp compiler is in fact a "compiler driver" whose task is to conduct various hardcoded compilation steps, of which calling libtool is simply the last one. And unfortunately the way it does it all in sequence is hardcoded, and AFAIK it's neither interruptible nor resumable.
To make it able to support this would require reverse-engineering, and at this point it would be probably saner to start an alternate implementation of il2cpp.exe from scratch.
I understand this problem prevents you from building your project, unfortunately there's little I can do on my side...
Perhaps an awful trick that could possibly work would look like this :
have il2cpp run (and obviously fail), prevent it from deleting its intermediary files on failure (by means to be determined), then take these intermediary object files and bundle them together in a static library by calling libtool yourself, and at this point resume the build.
Calling libtool ourselves and resuming the build is just a matter of editing the build.cmd master script, but preventing il2cpp from deleting its intermediary files would probably require some binary patching. Or perhaps setting a "no delete" flag or NTFS ACL permission on its intermediary output folder *while* it's running and before it fails... I don't like fragile hacks like those and would only consider investigating that if Unity doesn't provide the promised fix.
