Fix a bug in ABot handling in CoreArity
See Note [ABot branches: use max] in CoreArity. I stumbled on this when investigating something else, and opened Trac #13031 to track it. It's very hard to tickle the bug, which is why it has lurked so long, but the test stranal/should_compile/T13031 does so Oddly, the testsuite framework doesn't actually run the test; I have no idea why.
Showing with 33 additions and 4 deletions