This rolls forward the change introducing Int8# and Word8#
and fixes the problems discovered on 32-bit x86.
Interesting, did the register allocator ever actually use %ebp? It's mapped to Sp on i386, so I wouldn't expect it to be available for allocation most of the time. Perhaps in a very few places where we're returning from a foreign call and about to load Sp.
I didn't actually observe this. I just noticed this code when debugging and since the Note explicitly mentioned 8-bit registers, I thought it's better to make sure %ebp is also excluded.