PHEW!
Bug fixed.
Thanks for reporting it.
This bug made me also look into something I've been wanting to look into for a while now: I noticed XCode reporting compiling 16 files when it should be compiling 8 and so on; and taking noticeable longer to compile than when building for macOS targets. I thought maybe we accidentally were building for the simulator, but that did not make sense since the simulator would throw out compiler errors with Metal.
Now thanks to this bug I noticed we were building for both arm64 and armv7 (and also armv7s). Ogre 2.1+ only supports arm64 because those are the only devices that support Metal.
Even if GLES3 were to work on iOS again, these devices are slow and have very little RAM available (unlike modern Android equivalents which have terrific Hardware specs coupled with the horribly limited GLES 3.0 API) which means I doubt Ogre 2.1+ would be useful there. Maybe in the future someone will want to maintain it, but we'll cross that bridge when we get there.
The build error was coming when building for armv7, which apparently defines __thumb__ but does not actually support
Thumb. Probably some CMake -> XCode configuration shenanigan, or an XCode side effect of Apple no longer caring about these architectures.
Anyway I didn't pay much attention to it as I just disabled armv7.
This revealed another compiler error in debugbreak.h, this time for arm64, but it was very easy to fix.
Btw, build times for iOS are now literally halved thanks to not wasting time building for the unused armv7 platform.
Cheers
Matias